Joining method and device produced by this method and joining unit

ABSTRACT

A practical bonding technique is provided for solid-phase room-temperature bonding which does not require a profile irregularity of the order of several nanometers, in which a high-vacuum energy wave treatment and continuous high-vacuum bonding are not required. 
     Since an adhering substance layer is thin immediately after a surface activating treatment using an energy wave, a bonding interface is spread by crushing the adhering substance layer to perform bonding, so that a new surface appears on a bonding surface, and objects to be bonded are bonded together. In order to crush the adhering substance layer more easily, a bonding metal of a bonding portion of the object to be bonded needs to have a low hardness. According to the results of various experiments conducted by the present inventors, it was found that the hardness of the bonding portion which is a Vickers hardness of 200 Hv or less is particularly effective for room-temperature bonding.

TECHNICAL FIELD

The present invention relates to a bonding technique for bonding aplurality of objects to be bonded having a metal bonding portion at roomtemperature.

BACKGROUND ART

Conventionally, room-temperature bonding methods are performed in avacuum as described in Patent Document 1 or in inert gas as described inPatent Document 2 after a bonding surface is cleaned using an energywave. This is because, if the bonding surface is exposed to theatmospheric air, oxidation or readhesion of organic substances or thelike prevents metal atoms from being attracted by each other.

In the case of Patent Document 2, if gold is used, which does not react,oxidation is prevented, but adhesion of organic substances remains.Therefore, bonding is performed in inert gas.

The bonding surface is polished to a profile irregularity of the orderof several nanometers before being subjected to bonding under a lowload. This is because the profile irregularity of the order of severalnanometers can lead to spontaneous bonding due to intermolecular forcein a vacuum.

Patent Document 1: JP No. 2791429 B

Patent Document 2: JP No. 2001-351892 A

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

However, in conventional methods, bonding needs to be performed in avacuum, and at least in the atmospheric air, it is difficult to performbonding due to a readhesion film. Also, since bonding is performed onlyby contact under a low load, the profile irregularity needs to bereduced to the order of several nanometers, so that conventional methodsare not suitable for semiconductor wafers or chips after a plurality oftimes of a thin-film treatment or a heat treatment which undulate orhave a low profile irregularity.

Therefore, an object of the present invention is to provide a practicalbonding technique for solid-phase room-temperature bonding which doesnot require a profile irregularity of the order of several nanometers,in which a high-vacuum energy wave treatment or continuous high-vacuumbonding is not required.

Means for Solving Problem

To achieve the above-described object, a bonding method is provided forbonding objects to be bonded which have a bonding portion formed of ametal, in a solid phase at room temperature, by contacting the bondingportions with each other and pressing the bonding portions aftertreating the bonding portions with an energy wave which is an atom beam,an ion beam, or a plasma, wherein the bonding portion has a hardness of200 Hv or less.

A bonding apparatus according to the present invention comprises a headfor holding one of the objects to be bonded, a stage for holding theother object to be bonded, and a vertical drive mechanism capable ofperforming a pressing control with respect to at least one of the headand the stage in a direction substantially perpendicular to a bondingsurface of the object to be bonded, wherein the objects to be bondedwhich have a bonding portion formed of a metal are bonded together in asolid phase at room temperature by contacting the bonding portions witheach other and pressing the bonding portions after treating the bondingportions with an energy wave which is an atom beam, an ion beam, or aplasma, and the bonding portion has a hardness of 200 Hv or less.

As used herein, an energy wave treatment refers to a treatment whichactivates a bonding interface of objects to be bonded using an atombeam, an ion beam, or a plasma so as to achieve bonding at lowtemperature in a solid phase. This treatment may also be referred to asa surface activating treatment. The principle of bonding by surfaceactivation can be considered as follows. Specifically, assuming that anobject to be bonded is formed of a material, such as a metal, adheringsubstances, such as organic substances, oxide film, or the like, areremoved by etching from a bonding surface to generate an active danglingbond of a metal atom on the bonding surface, whereby the dangling bondsof the bonding surface of the objects to be bonded are bonded together.If the bonding surface is formed of gold, it is difficult for organicsubstances, an oxide film, or the like to adhere to the bonding surfaceafter a surface activating treatment, and bonding can be achieved if itis performed within several hours after the surface activating treatmentand even if not in a vacuum atmosphere.

As used herein, room-temperature bonding refers to a method forperforming bonding by heating at room temperature to a low temperatureof 180° C. or less, preferably at room temperature. Regardingconventional low-temperature bonding, lead-tin solder has a meltingpoint of 183° C. Therefore, bonding at 183° C. or less is effective.Bonding at 150° C. or less or at 100° C. or less is preferable, morepreferably at room temperature.

As described in Patent Document 1, by performing a surface activatingtreatment using an energy wave in a high vacuum of 10⁻⁵ Torr or less,adhering substances, such as organic substances, oxide film, or thelike, is removed from bonding surfaces (bonding portions) of objects tobe bonded, and the objects to be bonded can be bonded only by contactingdirectly if it is performed in a high vacuum. However, when objects tobe bonded are bonded in a low vacuum of 10⁻⁵ Torr or more or in theatmospheric air after cleaning, an adhering substance layer is formed onthe bonding surface, so that the objects to be bonded are not bondedonly by contacting directly. However, since the adhering substance layeris thin immediately after the surface activating treatment, a bondinginterface is spread by crushing the adhering substance layer to performbonding, so that a new surface appears on a bonding surface, and theobjects to be bonded are bonded together. In order to crush the adheringsubstance layer more easily, a bonding metal of a bonding portion of theobject to be bonded needs to have a low hardness. According to theresults of various experiments conducted by the present inventors, itwas found that the hardness of the bonding portion which is a Vickershardness of 200 Hv or less, preferably 20 Hv to 200 Hv, is particularlyeffective for room-temperature bonding (see FIG. 1).

FIG. 1 illustrates the result of a bonding strength comparisonexperiment regarding the hardness of the bonding portion. A surfaceactivating treatment was performed under the following experimentconditions: Ar plasma was used as an energy wave; and irradiation wasperformed with an intensity of 100 W for 30 seconds. After the surfaceactivating treatment, objects to be bonded were bonded together in an Aratmosphere by pressing. As a result, bonding was defective when thebonding portion was a Ni plating having a hardness of 300 Hv or achromium plating of 600 Hv. When copper, gold, or Al, which are metalshaving a Vickers hardness of 200 Hv or less, were used as the bondingportion, a satisfactory level of bonding strength was obtained. A morelimited region, i.e., a Vickers hardness range of 20 Hv to 200 Hv(connected with a curve line in FIG. 1) is considered as a satisfactorybonding region. Note that a region where bonding was achieved with astrength of 30 g/bump or more corresponding to 80% of the maximumstrength was determined to be a satisfactory bonding region, and aregion where bonding was achieved with a strength of 15 g/bump or lesswas determined to be defective bonding. When a wafer or the like issubjected to surface bonding, the strength is represented by a tensilestrength. In this case, bonding may be determined to be satisfactorywhen the strength is 20 MPa or more, and to be defective when thestrength is 10 MPa or less.

In the case of gold and copper, bonding was able to be achieved even inthe atmospheric air if bonding was performed immediately after a plasmatreatment. Particularly in the case of gold, the same level of bondingstrength remained in an Ar atmosphere even after one-hour exposure inthe atmospheric air. It was also found that, when objects to be bondedare bonded together, the objects to be bonded can be more firmly bondedtogether by applying a pressure of 150 Mpa or more to the objects to bebonded using a pressing means. In this case, when the metal constitutingthe bonding portion is gold, copper, or Al, bonding was able to beparticularly effectively achieved.

Assuming that objects to be bonded are formed of different materials,when these different materials are melted and diffused so as to performbonding, the resultant bonding is brittle, or weak in terms of thematerial. Therefore, when the present invention is applied to this case,the present invention is particularly effective since bonding can beachieved in a solid phase. When an object to be bonded is melted, themelted metal is not uniformly spread. In this case, when the object tobe bonded is solidified, a portion containing a larger amount pulls aportion containing a smaller amount, resulting in a position error.Therefore, bonding in a solid phase is effective.

Note that a process of performing surface activation with respect toobjects to be bonded using an energy wave and a process of bonding theobjects to be bonded may be performed in respective separateapparatuses, or in an integrated apparatus having a function ofperforming both the processes.

An energy wave emitting means for generating the energy wave may beprovided. In this case, it is assumed to use a means provided outsidethe apparatus. However, it is possible to perform a batch process fromthe surface activating treatment of objects to be bonded using theenergy wave to the bonding process of the objects to be bonded. As aresult, for example, it is possible to perform the surface activatingtreatment and the bonding process in a single chamber, thereby making itpossible to save the space of the apparatus.

In the bonding method and the bonding apparatus, during the time fromthe surface activating treatment to the bonding process of the objectsto be bonded, the objects to be bonded may not be exposed to theatmospheric air. With this configuration, the surface activatingtreatment of objects to be bonded to the bonding process are performedwithout exposure of the objects to be bonded to the atmospheric air,thereby preferably making it possible to prevent airborne matter or thelike from readhering to the objects to be bonded after surfaceactivation of the objects to be bonded.

A batch process from the surface activating treatment to the bondingprocess of objects to be bonded may be performed in the bondingapparatus. By performing the batch process from the surface activatingtreatment to the bonding process of objects to be bonded, it is possibleto prevent airborne matter or the like from readhering to the objects tobe bonded. In addition, if the surface activating treatment and thebonding process of objects to be bonded are performed in the samechamber, it is possible to further prevent airborne matter or the likefrom readhering to the objects to be bonded, and at the same time, it ispossible to achieve a compact size and a reduction in cost of thebonding apparatus.

The bonding portion may be formed of gold. With this configuration,particularly, gold has a low hardness and is not oxidized in theatmospheric air, so that it has less adhering substances. Thus, gold isan effective metal. As described below, bonding can be achieved even ifit is performed within several hours after exposure to the atmosphericair.

The bonding portion of the object to be bonded may be formed by forminga gold film on a surface of a base material having a hardness of 200 Hvor less, and after the objects to be bonded are bonded together, thegold film may be diffused into the base material. Thus, if the bondingsurface (a surface of the bonding portion) is formed of gold, it isdifficult for organic substances or the like to readhere to the bondingsurface after the energy wave treatment, and therefore, bonding can beachieved in the atmospheric air. If the gold film is diffused into thebase material after the objects to be bonded are bonded together, thebase materials are bonded together after bonding. Therefore, bonding canbe achieved using a uniform material having a high strength. Regarding amethod for diffusion, diffusion can be achieved even at room temperaturethough it takes a long time. Diffusion can be accelerated by heatingeven at low temperature. Note that diffusion indicates that particlesformed of molecules or atoms move or spread, and particles spread in anopposing material or a base material at a bonding interface.

In the bonding method and the bonding apparatus, gold or gold filmconstituting the bonding portion of at least one of the objects to bebonded may be caused to have a hardness of 100 Hv or less by annealing.As described above, in order to crush the bonding portion for copying,the bonding portion hardness is preferably reduced and softened.Therefore, the hardness of gold plating, which is typically 120 Hv ormore, is preferably reduced to 100 Hv or less by annealing, morepreferably 60 Hv or less.

The object to be bonded may be a semiconductor or a MEMS device in whichthe bonding portion comprises a plurality of metal bumps formed byforming a gold film on a surface of the base material (copper), andafter the objects to be bonded are bonded together, the gold film isdiffused into the base material (claims 4 and 30). In an electronicallyfunctioning device of a semiconductor or a MEMS device, it is desired tochange conventional Al electrodes to copper electrodes in terms ofcurrent-carrying capacity. However, it is practically difficult to use acopper bump because of its high bonding temperature. Therefore, bycovering a surface of a base material formed of copper with a gold film,bonding can be achieved at low temperature in gas or in the atmospherewhich are not vacuum. Thereafter, if gold is allowed to diffuse into thebase material, the coppers are bonded, thereby achieving the purpose.

The energy wave may be a low-pressure plasma. If the energy wavetreatment is assumed to be performed using an ion beam or an atom beam,a high vacuum atmosphere of about 10⁻⁸ Torr is required, resulting in aload to the equipment. By using a plasma, the energy wave treatment canbe achieved with the degree of vacuum of about 10⁻² Torr, resulting in asimple equipment. As a result, it leads to a compact size and areduction in cost of the apparatus. It is more preferable to use Ar asreaction gas for generating plasma, since Ar is inert and has a highetching capability. Also, it is preferable to reduce the pressure to10⁻³ Torr or less in order to remove the reaction gas or etched matterafter or during cleaning (energy wave treatment) of the object to bebonded. In order to remove the reaction gas, such as Ar implanted intothe bonding surface (bonding portion) of the object to be bonded, or thelike, heating can be performed at about 100 to 180° C. as well.

In the bonding method, at least one of the objects to be bonded may be asemiconductor, and the bonding portion of each of the objects to bebonded may be subjected to plasma cleaning using the low-pressure plasmawhich is generated with electric field having alternating + and −directions generated by an alternating power supply before the objectsto be bonded are bonded together in a solid phase at room temperature.

In the bonding apparatus, at least one of the objects to be bonded maybe a semiconductor, and the bonding portion of each of the objects to bebonded may be subjected to plasma cleaning using the low-pressure plasmawhich is generated with electric field having alternating + and −directions generated by an alternating power supply before the objectsto be bonded are bonded together in a solid phase at room temperature.

For example, assuming that at least one of the objects to be bonded is asemiconductor, if + ions or − electrons strike a circuit surface of thesemiconductor, charge-up damage occurs with respect to the circuit,particularly a gate oxide film or the like. To avoid this, the + ion andthe − electron are caused to alternately strike so as to neutralizebefore accumulating charge. Thereby, it is possible to avoid charge-updamage. If adhering substances are removed by etching from the bondingsurface by plasma, resulting in surface activation, bonding of a metal,Si, or an oxide can be achieved at low temperature in a solid phase.

In the bonding method and the bonding apparatus, the alternating powersupply may be changed evenly at more than 1:5. If the ratio ofalternately changing is even more than 1:5, charge-up damage can bereduced. More preferably, the ratio is even more than 1:2.

Regarding the alternating power supply, Vdc is a negative (−) value, andthe + region accounts for 20% to 40% in the bonding method and thebonding apparatus. Ar or oxygen plasma, or the like is a + ion.Therefore, in order to accelerate the + ion to strike and etch a surfaceto be cleaned, an electrode holding an object to be bonded needs to have− electric field. Therefore, the value Vdc is preferably negative (−).Here, Vpp indicates peak-to-peak of an alternating current waveform of avoltage, and Vdc indicates a bias voltage which is an offset value froma voltage value of 0 V which is the center of Vpp.

The alternating power supply is an RF plasma generating power supplycapable of controlling a value of the bias voltage Vdc. When the + and −of the alternating power supply are excessively even, the chance ofstrike of + ions is reduced, resulting in a reduction in cleaningcapability (surface activating capability). Also, charge-up damageoccurs due to − electrons. Therefore, preferably, when the value of Vdccan be adjusted to an optimum value for each application, optimumcleaning capability can be exhibited without causing charge-up damage.

When an RF plasma generating power supply which provides an alternatingcurrent as illustrated in FIG. 26 is used as an alternating powersupply, electric field can be alternately switched between + and −. Byadjusting the value of Vdc, the ratio of + and − can be easily adjusted.

The alternating power supply may be a pulsed wave generating powersupply capable of controlling a pulse width. As the alternating powersupply, a pulsed wave generating power supply illustrated in FIG. 27 canbe used. If a pulsed wave is used, steep rising and falling can beobtained, thereby increasing cleaning capability.

By adjusting a pulse width or interval as illustrated in FIG. 28 inaddition to the adjustment of the value of Vdc, the ratio of + and − orthe strike time can be managed. Therefore, finer setting can be achievedthan when an alternating RF plasma generating power supply is used, sothat it is easier to find an optimum value.

The degree of vacuum is preferably 10⁻³ Torr or less during, before, orafter plasma cleaning (energy wave treatment). In order to removeimpurities, cleaning is preferably performed after reducing the pressureto 10⁻³ Torr or less. Also, it is preferable to reduce the pressure to10⁻³ Torr or less in order to remove the reaction gas or etched matterafter or during cleaning of the object to be bonded. In order to removethe reaction gas, such as Ar implanted into the bonding surface, heatingcan be performed at about 100 to 180° C. as well. During the cleaning,reaction gas may be supplied from one side of the object to be bondedand the reaction gas may be sucked from the other side. With thisconfiguration, it is possible to flow the reaction gas on the bondingsurface in one direction. Therefore, adhering substances scatteredduring plasma cleaning can be efficiently removed, thereby making itpossible to effectively suppress removed matter from readhering to theobject to be bonded.

The head and the stage of the present invention each comprise anobject-to-be-bonded holding means. In order to achieve uniform bondingwithout unbalanced bonding, an elastic material is preferably providedon a surface of at least one of the object-to-be-bonded holding means,and pressing is preferably performed via the elastic material withrespect to both objects to be bonded when the objects to be bonded arebonded together. In the bonding method of the present invention, sincemetal bonding is performed in a solid phase (i.e., bonding is notperformed using melted solder), bonding can be achieved only at acontact portion if the parallelism or the flatness is not sufficientbetween the objects to be bonded. Therefore, an elastic material may beprovided on a surface of at least one of the objects-to-be-bondedholding means, and pressing may be performed via the elastic materialwith respect to both the objects to be bonded. Thereby, it is possibleto increase the parallelism of the objects to be bonded. Also, it ispossible to increase the flatness if an object to be bonded is thin.Also, after the objects to be bonded are contacted with each other, anelastic material may be inserted between the object to be bonded and theobject-to-be-bonded holding means.

At least one of the object-to-be-bonded holding means is preferably heldby a spherical bearing, and objects to be bonded are preferablycontacted and pressed by each other during or before bonding so that thetilt of at least one of the objects to be bonded can match the tilt ofthe other. The object-to-be-bonded holding means may be held on thestage and/or the head via a spherical bearing, and the objects to bebonded may be contacted and pressed by each other during or beforebonding so that the tilt of at least one of the objects to be bonded canmatch the tilt of the other. With such a configuration, bonding can beperformed after increasing the parallelism of the objects to be bonded(see FIG. 29). The spherical bearing may have a lock mechanism whichselects lock/free, and is normally in a locked state, and when copying,is in a free state. The spherical bearing can be locked after theparallelism is once increased, and while holding this state, objects tobe bonded can be subjected to a plasma treatment (energy wave treatment)and alignment, followed by bonding. Therefore, since alignment isperformed after increasing the parallelism, the objects to be bonded canbe preferably bonded together without a position error.

In the method and the bonding apparatus, an ultrasonic vibration headcomprising a horn, a horn holding section, and an oscillator may beprovided, and ultrasonic vibration having an amplitude of 2 μm or lessmay be applied to objects to be bonded in the atmospheric air duringbonding, so that metal bonding is performed in a solid phase, where aload is 150 MPa or less and heating is at 180° C. or less. When bondingis performed in the atmospheric air, bonding is more easily achieved byapplying ultrasonic vibration. Since surface activation has already beenperformed, only a small level of ultrasonic energy is required, i.e., anamplitude of 2 μm or less which can suppress damage and position error,is sufficient. More preferably, the amplitude is 1 μm or less. Also, byapplying ultrasonic waves, a bonding load can be reduced by half, i.e.,to 150 MPa or less. When bonding is performed with respect to a metal(gold) protrusion, bonding can be achieved using a pressing force of ashigh as about 300 MPa at room temperature. If a bump is present on asemiconductor circuit surface, some circuits are generally damaged with200 MPa or more. Experiments were conducted under the followingconditions: a gold bump (metal protrusion) having 50 μm square and 20 μmin height is provided on a semiconductor chip, where a variation in bumpheight is 1 μm, and the semiconductor chip is bonded onto a thin goldfilm substrate using ultrasonic waves (ultrasonic bonding) or at roomtemperature (room-temperature bonding). In the case of theroom-temperature bonding, bonding was achieved when the load was 80g/bump or more. In the case of the ultrasonic bonding, bonding wasachieved when the load was 40 g/bump or more. Therefore, the bump needsto be crushed by 1 μm or more as a crushed bump amount. When a bumphaving a height of 20 μm is produced by gold plating, the lower limit ofa variation in height is 1 μm. Therefore, it is necessary to crush thebump in such an amount.

Between the cleaning in a reduced pressure and the bonding in theatmospheric air, at least one of the objects to be bonded is transportedinto a cleaning chamber, which is linked to a transport means fortransporting the objects to be bonded to a bonding section aftercleaning, and the next objects to be bonded are cleaned during bonding.Objects to be bonded whose bonding surfaces are formed of gold or coppercan be previously separately surface-activated by a plasma treatment ina vacuum chamber, and can be removed into the atmospheric air, followedby bonding. The cleaned objects to be bonded are transported to abonding section by a transport means, and the next objects to be bondedare cleaned during bonding. Therefore, cleaning can be performedparallel to bonding, thereby making it possible to save time. Whenbalance is not attained on a one-by-one basis, a plurality of objects tobe bonded may be placed on a tray or the like and may be simultaneouslycleaned. When a continuous object to be bonded is provided on a reel,the object to be bonded may be seized via a packing by a chamber door soas to be subjected to a plasma treatment.

The bonding portion of at least one of the objects to be bonded may havea surface roughness Ry of 120 nm or more. As used herein, the surfaceroughness indicates minute irregularities in a predetermined area,excluding undulating pattern. For example, the surface roughness isrepresented by a highest value and a smallest value of minuteirregularities in 10 μm². As described in Patent Document 1, by cleaningobjects to be bonded in a vacuum using an energy wave, adheringsubstances, such as organic substances, oxide film, or the like, isremoved from the bonding surface, and the objects to be bonded can bedirectly bonded together if it is performed in a vacuum. However, aftercleaning, if bonding is performed in the atmospheric air or a low vacuumwhich have much airborne matter, an adhering substance layer is formedon the bonding surface, so that the objects to be bonded cannot bebonded if they are directly contacted with each other. However, sincethe adhering substance layer is thin immediately after cleaning, bondingcan be achieved by the following method. This is because, as illustratedin FIG. 2A, by providing minute irregularities on the bonding surface,the convex portions are crushed by pressing to be spread, so that a newsurface appears and bonding is achieved (see FIG. 2B). When viewedmicroscopically, crystal orientations arranged as illustrated in FIGS.3A and 3B are rotated by the convex portion being crushed, so that thenew surface appears. As can be seen from FIG. 4, when the surfaceroughness (minute irregularities) is 120 nm or more, a sufficientbonding strength is obtained. This is measured as follows. Metalprotrusions (a plurality of bumps) are provided on an object to bebonded, a shear strength is measured after bonding, and a shear strengthper bump is indicated. A bump which was formed of gold plating and was40 μm square and 15 μm in height, was used. As a guide, a sufficientshear strength was assumed to be 30 g/bump corresponding to 80% of amaximum strength.

In the bonding method and the bonding apparatus, at least one of thebonding surfaces preferably has a surface roughness Ry of 120 nm or moreand 2 μm or less. If irregularities on the bonding surface (bondingportion) of the object to be bonded are excessively large, a contactarea becomes small since the maximum crushed amount is not more thanabout several micrometers, resulting in a reduction in bonding strength.As illustrated in FIG. 4, if the surface roughness is 2 μm or more, asufficient bonding strength is not obtained. Thus, it is found that thesurface roughness is preferably 120 nm or more and 2 μm or less.

In the bonding method and the bonding apparatus, the bonding surface ofthe object to be bonded may be a plurality of metal protrusions, and thetip may be in a convex shape. In the case where surfaces are bondedtogether, even when a plurality of convex-shaped bonding portions areused so as to cause the micro irregularities to be effective asdescribed above, the bonding area is smaller than that of surfacebonding, but a similar effect is obtained.

In the bonding method and the bonding apparatus, Ar plasma (reactiongas: Ar gas) may be used as an energy wave when objects to be bonded aresubjected to a surface activating treatment, and the bonding surfaces ofthe objects to be bonded may be etched using the Ar plasma to roughenthe bonding surfaces. When Ar plasma is used to clean a bonding portion,a rough bonding surface is obtained by setting a cleaning time to belonger (e.g., three minutes, where an ordinary time is 30 seconds). Theroughness can be effectively caused to be 120 nm or more.

The bonding method may comprise a head for holding one of the objects tobe bonded, a stage for holding the other object to be bonded, and avertical drive mechanism for performing a position control with respectto at least one of the head and the stage in a direction substantiallyperpendicular to the bonding surface of the object to be bonded, andperforming a pressing control, wherein, when the objects to be bondedare bonded together, during the bonding, the vertical drive mechanismmay be driven to press the objects to be bonded, and thereafter, thevertical drive mechanism may be stopped to hold a constant height of thehead from the stage for a predetermined time.

In the bonding apparatus, the vertical drive mechanism may be capable ofperforming a position control with respect to at least one of the headand the stage in a direction substantially perpendicular to the bondingsurface of the object to be bonded, and when the objects to be bondedare bonded together, during the bonding, the vertical drive mechanismmay be driven to press the objects to be bonded, and thereafter, thevertical drive mechanism may be stopped to hold a constant height of thehead from the stage for a predetermined time.

As used herein, the height of the head from the stage indicates adistance between objects to be bonded during a process which presses anobject to be bonded held by the head against an object to be bonded heldby the opposing stage to microscopically crush the bonding portion. Tokeep constant the height of the head from the stage means to keepconstant the distance between the objects to be bonded. In the casewhere the objects to be bonded are bonded, when pressing isinstantaneously performed with respect to the objects to be bonded,irregularities of the bonding surface are elastically deformed, so thatcrystal at the interface may not be rotated. Also, the elasticdeformation remains as residual stress which acts in a direction whichcauses the object to peel off, rather than bonding force, resulting in areduction in bonding strength. Regarding a method for preventing this,the head height is kept constant for a predetermined time, so that thecrystal cannot endure a load at the bonding interface as viewedmicroscopically, and therefore, crystal orientations are rotated orparticles are moved. As a result, a new surface appears and bonding isperformed, and the movement of particles removes the residual stress.During the pressing control, the height is being more and more reduced,and elastic deformation invariably occurs, so that the crystalorientation is not displaced. However, if the height remains constant,the crystal orientation starts being displaced from the elasticdeformation, and successively collapses over time. Thereby, a newsurface appears, contributing to bonding.

In the bonding apparatus, a head height detecting means may be providedin the head section positioned at a tip of the vertical drive mechanismso as to control the height when the head is stopped. A head heightdetecting means may be provided so as to keep constant the head heightof the order of submicrons. When viewing the bonding interfacemicroscopically, in the elastically deformed bonding interface, elasticdeformation is released due to rotation of crystal orientations ormovement of particles. If an elastically deformed portion coincides witha ball or the like of a bolt-nut mechanism of a Z lifting/loweringmechanism (vertical drive mechanism), the elastic deformation mode iscaused by further pressing even when a drive motor is stopped. To avoidthis, a height detecting means is provided to the head section so as tokeep constant the height of the order of submicrons. Thereby, elasticdeformation is gradually released, leading to an increase in bondingstrength. FIG. 5 illustrates an increase in bonding strength after thehead is stopped.

Note that the head structure capable of a pressing control and aposition control can be composed of a ball screw in which pressuredetecting means are arranged in series, and a servo motor. The headstructure can also be composed of a cylinder in which a positiondetecting means is provided, and a servo valve, thereby making itpossible to perform a pressing control and a position control. Note thatthe present invention is not limited to this, and any pressing means andposition control means may be used as long as a pressing control and aposition control can be achieved.

In the bonding method and the bonding apparatus, the stop time may beone second or more. Regarding the stop time, as illustrated in FIG. 5,an effect was obtained in the case of one second or more, and a changedid not occur in the case of two minutes or more, depending on thematerial or the bonded state.

In the bonding method and the bonding apparatus, a heating means may beprovided so as to heat at 180° C. or less when the head is stopped. Byheating when the head is stopped, rotation of crystal orientations ormovement of particles is efficiently performed, so that bonding isdeveloped and residual stress is removed, resulting in an increase inbonding strength. FIG. 6 illustrates heating temperature and bondingstrength when the head is stopped. Regarding heating temperature,low-temperature heating at 180° C. or less was sufficient.

In the bonding method, after the bonding portion of at least one of theobjects to be bonded is subjected to leveling, the bonding portion ofeach of the objects to be bonded may be treated with the energy wave,and thereafter, the objects to be bonded may be bonded together in asolid phase at room temperature.

In the bonding apparatus, after the bonding portion of at least one ofthe objects to be bonded is subjected to leveling, the bonding portionof each of the objects to be bonded may be treated with the energy wave,and thereafter, the objects to be bonded may be bonded together in asolid phase at room temperature.

With this configuration, as illustrated in FIG. 7, room-temperaturebonding can be achieved by pressing even in the atmospheric air if theobjects to be bonded are not allowed to stand after dry cleaning (energywave treatment). This may be because, although a thin attached layer isformed on the bonding surface, the layer is so thin that it can becrushed by pressing. When bonding is performed at room temperature, aload about two times higher than when heating is performed is requiredto crush and contact bumps. However, in the case of leveled bumps, asufficient bonding strength can be obtained using a pressing force of150 MPa, while a pressing force of 300 MPa is required when leveling isnot performed. This is because it is necessary to crush a roughness orthe like of the bonding surfaces of objects to be bonded so as tocertainly contact the objects to be bonded together, and thus a pressingforce is required depending on a variation in the bump height or themagnitude of the surface roughness. In the case of an ordinary bump, theheight variation was 2 μm However, after performing leveling, both theheight variation was 120 nm or less. Therefore, it is considered thatthe bonding load was able to be reduced. As used herein, the leveling,with reference to the surface roughness of the bump surface of FIG. 8and the variation in height between each bump of FIG. 9, indicates thatthe height or surface roughness of a bump is corrected to be uniform bypressing the bump against a smoothing means, such as a reference supportor the like, having a high flatness as illustrated in FIG. 10. Afterleveling, as illustrated in FIG. 11, the objects to be bonded are bondedtogether. Although a chip having a bump and a substrate having a pad areillustrated in this example, other objects to be bonded may be used.

The leveling may be performed using an opposing object to be bondedbefore the objects to be bonded are bonded together. With thisconfiguration, since leveling is performed using an opposing object tobe bonded, leveling can be achieved to fit features (irregularities) ofthe surface of the object to be bonded. Therefore, it is possible toreduce a bonding load for an object to be bonded having a low flatness.For example, in the case of a build-up substrate having wiring layersstacked up, a slight difference occurs in the height of an upperelectrode pad, depending on a lower wiring pattern.

In the bonding method and the bonding apparatus, both objects to bebonded may have a metal bump (bonding portion), and the metal bumps maybe bonded together after leveling. Preferably, when both the objects tobe bonded are leveled, the bonding surfaces are contacted with eachother without irregularities, resulting in a further reduction inbonding load. The bonding load was able to be reduced to 100 MPa or lessas measured in FIG. 7.

In the bonding method, in a chamber having a reduced pressure, while thebonding surfaces of the objects to be bonded are not placed facing eachother, the bonding portions may be treated with the energy wave, andthereafter, at least one of the objects to be bonded may be moved sothat the bonding surfaces are placed facing each other, and thereafter,at least one of the objects to be bonded may be moved in a directionsubstantially perpendicular to the bonding surface to contact thebonding portions with each other, and bond the objects to be bondedtogether in a solid phase.

The bonding apparatus may comprise, in a vacuum chamber, the head, thestage, the vertical drive mechanism, and a moving means for moving atleast one of the head and the stage in a side direction, wherein theenergy wave emitting means may be capable of performing the energy wavetreatment with respect to each of the objects to be bonded separately.In the vacuum chamber having a reduced pressure, while the moving meanscauses the bonding surfaces of the objects to be bonded not to be placedfacing each other, the bonding portions may be treated with the energywave, and thereafter, at least one of the objects to be bonded may bemoved so that the bonding surfaces are placed facing each other, andthereafter, at least one of the objects to be bonded may be moved by thevertical drive mechanism in a direction substantially perpendicular tothe bonding surface to contact the bonding portions with each other, andbond the objects to be bonded together in a solid phase.

Conventionally, when an energy wave treatment is performed while bothobjects to be bonded are placed facing each other, adhering substancesetched on one of the objects to be bonded readhere to the other.Therefore, in the present invention, while the bonding surfaces of theobjects to be bonded are not placed facing each other, the bondingportions are subjected to the energy wave treatment, and thereafter, theobjects to be bonded are shifted to a position where they face eachother, followed by bonding. Thereby, it is possible to prevent theabove-described adhering substances from readhering. By performingplasma cleaning (treatment) while the stage is slid to a standbyposition, etched adhering substances are prevented from being scatteredto an opposing surface and readhering to the other object to be bonded.

In the bonding method and the bonding apparatus, the degree of vacuummay be 10⁻³ Torr or less during the plasma cleaning (treatment).Preferably, when the degree of vacuum is 10⁻³ Torr or less, scatteredmatter strikes ions so that the direction is changed, resulting in areduction in probability of readhering.

In the bonding method and the bonding apparatus, a gap between theobjects to be bonded after being slid to the bonding position may be 20mm or less. Conventionally, plasma generation requires at least about 30mm between the upper and lower objects to be bonded. Therefore, when thehead is lowered, a position error occurs irrespective of alignment dueto the tilt or play of the Z axis (vertical drive mechanism). However,by generating a plasma on each of the head and the stage while the stageis slid to the standby position, the movement distance of the Z axis canbe minimized, so that the distance between the objects to be bonded canbe set to be 20 mm or less which is smaller than conventional 30 mm orless. More preferably, the distance can be set to be 5 μm or less. Whenthe distance is suppressed to several micrometers or less, an error dueto the tilt of the Z axis is negligible, so that an error in ahorizontal direction due to the Z movement can be minimized inproportion to the movement amount.

Since plasma can be generated after the objects to be bonded are slid, ametal is provided on a surface opposed to the object to be bonded, andthe metal is used as a plasma electrode, so that the metal is sputteredon the surface of the object to be bonded, and a thin film is formed. Byproviding a metal film on the surfaces of both the objects to be bondedby sputtering, the metals can be bonded together. As a result, Al,ceramics, oxides, and the like can be used which are difficult toachieve bonding by conventional surface activation, so as to achievebonding. When the bonding surface of the object to be bonded ispreviously etched and cleaned using the object to be bonded as a plasmaelectrode before the above-described sputtering, bonding can be moreeasily achieved. Alternatively, while the objects to be bonded areplaced facing each other after being slid, one object to be bondedhaving a metal surface can be used as an electrode and sputtered withrespect to the other object to be bonded. Particularly, it is suitablewhen one object to be bonded has a metal, such as gold or copper, whichcan easily allow bonding, and the other has a material which isdifficult to achieve bonding.

When the bonding portion is treated with the energy wave, a metalelectrode may be provided at a position facing the bonding surface of atleast one of the objects to be bonded, a metal film including a metalforming the metal electrode may be formed on the bonding surface of theobject to be bonded by sputtering, and the objects to be bonded may bebonded together in a solid phase.

In the bonding method and the bonding apparatus, a metal film may beformed on the bonding surface of the other object to be bonded formed ofa hard metal (Ni, etc.), an oxide, Si, or a ceramic, and the metals maybe bonded together in a solid phase. A metal to be sputtered is providedat a position facing the bonding surface of the object to be bonded, andthe metal is irradiated with an energy wave, so that the metal issputtered onto the surface of the object to be bonded and a thin film isformed. If a metal film is sputtered onto the surfaces of both theobjects to be bonded, the metals can be bonded together in a solidphase. A hard metal (Ni, etc.), a ceramic, an oxide, Si, and the likewhich are difficult to achieve bonding by conventional surfaceactivation can be used to achieve bonding. When the energy wave is alow-pressure plasma, sputtering can be performed by using the metal asthe plasma electrode. When the bonding surface of the object to bebonded is etched and cleaned (energy wave treatment) by using the objectto be bonded as the plasma electrode before sputtering, bonding can beeasily achieved. Alternatively, while the objects to be bonded areplaced facing each other, one object to be bonded having a metal surfaceis used as an electrode, so that sputtering can be performed withrespect to the opposing other object to be bonded. Particularly, it issuitable when one object to be bonded has a metal formed of gold orcopper which easily achieve bonding, and the other object to be bondedis formed of a material which is difficult to achieve bonding.

In the bonding method and the bonding apparatus, when surface activationis performed using an energy wave, the surface metal formed of gold orcopper of one object to be bonded may be sputtered to form a metal filmformed of gold or copper on the bonding surface of the other object tobe bonded, and room-temperature bonding may be achieved in a solid phasein the atmospheric air. When the metal to be sputtered is gold orcopper, room-temperature bonding can be achieved in a solid phase in theatmospheric air.

The bonding portion may be formed in the shape of a contour, the bondingportion is surface-activated with the energy wave, and thereafter, theobjects to be bonded may be bonded together in a solid phase at roomtemperature, so that space surrounded in the shape of contour by thebonding portions may be formed between the bonding surfaces of theobjects to be bonded to enclose a predetermined atmosphere in the space. With this configuration, when the bonding portion is formed of ametal, the objects to be bonded can be bonded together in a solid phaseat low temperature ranging from room temperature to 180° C. afterperforming etching using an energy wave (surface activating treatment).As compared to solder which conventionally allows metal bonding at lowtemperature, bonding can be achieved at 183° C. (the melting point ofsolder) or less, even 150° C. or less. The objects to be bonded can bebonded in a vacuum atmosphere or in a filling gas atmosphere. Thereby,the steps of bonding, evacuation, gas replacement, and enclosing can beperformed in one process using a single apparatus. In addition, sincethe surface (bonding portion) is activated by etching using an energywave, and bonding is performed by atomic force, bonding can be achievedat room temperature. Although the bonding strength is increased byheating at about 150° C. as well, room-temperature bonding can achieve abonding strength higher than that of conventional heating-diffusionbonding. Note that the surface activation treatment of the objects to bebonded using an energy wave and the process of bonding the objects to bebonded together may be performed by respective separate apparatuses.

In the bonding method and the bonding apparatus of the presentinvention, the surface activating treatment to the bonding may beperformed without exposing the objects to be bonded to the atmosphericair. With this configuration, since the surface activation to thebonding is performed without exposure to the atmospheric air, it ispreferably possible to prevent airborne matter from readhering to theobjects to be bonded after the surface activation.

In the bonding apparatus of the present invention, the surfaceactivation to the bonding may be performed as a batch process. Byperforming the surface activation to the bonding of the objects to bebonded as a batch process, it is possible to further prevent airbornematter from readhering. If the surface activation and the bonding areperformed in the same chamber, it is possible to further preventairborne matter from readhering, and at the same time, a compact sizeand a reduction in cost can be achieved.

If the bonding portion is formed of gold, the bonding portion is notcorroded or gas is not generated. Therefore, gold is preferable as anenclosing material for enclosing an atmosphere. Also, since gold has aconsiderably high melting point, gold has a high level of reliability athigh temperature after bonding is performed at low temperature in asolid phase. Thus, when gold is used, bonding can be achieved in theatmospheric air or in filling gas if it is performed within apredetermined time after surface activation. In the present invention,gold may be used only in the bonding surface. Regarding a portion whichrequires a high height, a soft material can be selected as the basematerial of the bonding portion.

The bonding portion may be formed of gold, or a gold film on a surfaceof a base material having a hardness of 200 Hv or less, and the gold orthe gold film constituting the bonding portion of at least one of theobjects to be bonded may be a gold plating having a thickness of 1 μm ormore. With this configuration, regarding a method for absorbing theundulating pattern or surface roughness of the bonding surface (bondingportion) of an object to be bonded, gaps can be filled by at least oneof the bonding surfaces being crushed by a certain height, resulting incopying. Therefore, the gold of one object to be bonded is effectivelyplated to 1 μm or more.

Bonding is performed in a vacuum, so that a vacuum atmosphere isenclosed in the space. With this configuration, the bonding method forthe objects to be bonded is etching (surface activating treatment) forthe bonding portion in a vacuum using an energy wave. Therefore, it ispreferably possible to easily enclose a vacuum atmosphere in the space.Also, if the surface activation and the bonding are performed in thesame chamber, bonding is preferably performed directly in the vacuumatmosphere of the surface activation.

After the surface activation of the bonding portion, a vacuum state of areduced pressure chamber may be replaced with filling gas, and theobjects to be bonded may be bonded in the filling gas to enclose thefilling gas atmosphere in the space.

The bonding portion which is formed of gold is not corroded and adhesionof foreign matter is suppressed for a predetermined time even if bondingis not performed in a vacuum or in inert gas. Therefore, there is not aninfluence on bonding even if bonding is not performed in a vacuum.Therefore, other gases as well as inert gas can be preferably applied tothe present invention.

Note that the filling gas may be Ar or nitrogen in the bonding methodand the bonding apparatus. Preferably, if the filling gas is Ar ornitrogen, there is not an influence (corrosion, etc.) on the device. Ifthe filling gas is Ar, a reaction gas atmosphere used for bonding ispreferably used directly.

Regarding the surface activating treatment using an energy wave, sinceadhering substances present on the surface of the object to be bondedadhere by 1 nm or more for several seconds if the surface is exposed tothe atmospheric air after wet cleaning, it is effective to etch by atleast 1 nm or more.

In the bonding method and the bonding apparatus of the presentinvention, gold included in the bonding portion of at least one of theobjects to be bonded may be annealed to have a hardness 100 Hv or less.

As described above, it is preferable to reduce and soften the hardnessof the bonding portion so as to crush and cause the bonding portion toperform copying. Therefore, the hardness of gold which is normally 120Hv or more is caused by annealing to be 100 Hv or less. Also, 60 Hv orless is more preferable.

Preferably, if the object to be bonded is a wafer, a plurality ofdevices can be simultaneously bonded together with a batch process. Thewafer is diced into pieces after bonding.

In the bonding method and the bonding apparatus of the presentinvention, the object to be bonded may be a device including a surfaceelastic wave device, a RF device, or the like. A semiconductor deviceincluding a semiconductor device, a surface elastic wave device, a RFdevice, and the like, a MEMS device having a mechanical movable portion,and the like particularly require enclosing. Also, these are susceptibleto heat, and are formed of a combination of different materials.Therefore, a distortion occurs due to thermal expansion, and thesedevices cannot endure bonding at high temperature. Therefore, thepresent invention is preferable to these devices. There is not aconventional bonding method at 200° C. or less for these devices whichis susceptible to gas from a resin or moisture. Also, since thesedevices have vibrating surfaces and MEMS has a mechanically movingactuator, it is not possible to perform attachment using a resin, anddirect bonding is required. Therefore, the present invention ispreferable to these devices. As a form, attachment by handling on awafer during a semiconductor production process is most effective, andthe present invention is also suitable for a chip state after dicing.

The objects to be bonded may be bonded together in the atmospheric air.With this configuration, since the adhering substance layer is thinimmediately after the surface activating treatment, the bondinginterface is spread by crushing the adhering substance layer so as toperform bonding, so that a new surface appears on the bonding surface,and the objects to be bonded are bonded together even in the atmosphericair. Regarding time, after the surface activating treatment,particularly in the case where the bonding portion is formed of gold, itis difficult for oxides, organic substances, and the like to readhere,and therefore, bonding is easily achieved if it is performed within onehour.

According to experimental results, required heating temperature dependson an elapsed time after the energy wave treatment of the bondingportion, the type of gas, a moisture content (humidity). If mounting(bonding) is performed within one hour after exposure to the atmosphericair, bonding was able to be achieved by heating at 100° C. or less. Inthe bonding method, although bonding is performed in a solid phase,metal molecules are directly coupled with each other on the bondingsurface. Therefore, even if heating is performed at high temperature(e.g., 350° C.) after bonding, the metal molecules are only diffused,and the bonding strength does not decrease, or the resistance value doesnot increase. Thus, high reliability is obtained even at hightemperature.

One of the objects to be bonded may be an electrically functioningdevice which employs the bonding portion as an electrode, and thebonding portion may have a surface formed of gold or copper, the bondingportion of the object to be bonded may be cleaned with the energy wave,and thereafter, an attached layer may be formed on the bonding portionusing gas, the bonding portions including an metal electrode may becontacted with each other in the atmospheric air, the positions of theobjects to be bonded may be adjusted to optimum positions while thedevice is caused to electrically function, and thereafter, the objectsto be bonded may be bonded together in a solid phase at roomtemperature.

One of the objects to be bonded may be an electrically functioningdevice which employs the bonding portion as an electrode. The bondingapparatus may comprise the head for holding the functioning device, thestage for holding the other object to be bonded, the vertical drivemechanism for vertically moving at least one of the head and the stage,a probe for causing the functioning device to electrically function, arecognizing means for recognizing a function of the functioning device,and an alignment table for correcting relative positions of thefunctioning device and the object to be bonded. The bonding portion mayhave a surface formed of gold or copper, the bonding portion of theobject to be bonded may be cleaned with the energy wave, and thereafter,an attached layer may be formed on the bonding portion using gas, thebonding portions including an metal electrode may be contacted with eachother in the atmospheric air, the positions of the objects to be bondedmay be adjusted to optimum positions while the device is caused toelectrically function, and thereafter, the objects to be bonded may bebonded together in a solid phase at room temperature (claim 46).

In order to mount a functional device while adjusting the positionthereof with high efficiency and high accuracy, it is effective toperform metal bonding with respect to a metal electrode by heating afterperforming position adjustment while the functional device is beingdirectly caused to electrically function, where a metal electrode iscontacted during mounting. As in conventional techniques, once analignment mark is used instead, an error is included and the efficiencyis reduced due to complication. Therefore, the surface of the bondingportion of the functional device (object to be bonded) is formed of goldor copper, both bonding surfaces are treated with an energy wave, suchas an atom beam, an ion beam, or a plasma, in a vacuum, and thereafter,an attached layer is attached to the bonding portion using gas, thebonding portions formed of a metal electrode are contacted with eachother in the atmospheric air, the functional device is adjusted to anoptimum position while being caused to electrically function, andthereafter, metal bonding is performed in a solid phase by heating at180° C. or less.

As a method for bonding metals in a solid phase at room temperature, amethod of treating bonding surfaces formed of gold with an energy wavein a vacuum, and bonding the bonding surfaces together in an inert gasatmosphere, is effective. However, if the bonding surfaces are contactedwith each other, the bonding surfaces are bonded together. Therefore,after the energy wave treatment, an attached layer is once formed usinggas, so that the metal electrodes are not bonded only by contacting themwith each other in the atmospheric air. Therefore, relative positions ofthe functional device and the object to be bonded can be adjusted whilethe functional device is caused to electrically function. Aftercompletion of the position adjustment, both the metal electrodes arebonded only by low-temperature heating at 180° C. or less. Thus, thetemperature can be set to be lower than 183° C. which is the meltingpoint of lead-tin solder for conventional low-temperature metal bonding.In order to suppress a position error due to heating to a small level,150° C. or less is preferable. 100° C. or less is more preferable.

When solder is melted, the melted solder is not uniformly spread. Inthis case, when the solder is solidified, a portion containing a largeramount of solder pulls a portion containing a smaller amount of solder,resulting in a position error. Therefore, if objects to be bonded(functional devices) can be bonded together in a solid phase, it iseffective. According to data, required heating temperature depends on anelapsed time after the energy wave treatment of the bonding portion, thetype of gas, and a moisture content (humidity). If mounting is performedwithin one hour after exposure to the atmosphere (forming an attachedlayer), bonding was able to be achieved by heating at 100° C. or less.In the bonding method, although bonding is performed in a solid phase,metal molecules are directly coupled with each other on the bondingsurface. Therefore, even if heating is performed at high temperature(e.g., 350° C.) after bonding, the metal molecules are only diffused,and the bonding strength does not decrease, or the resistance value doesnot increase. Thus, high reliability is obtained even at hightemperature.

Regarding the gas for attaching an attached layer, when gas containingnitrogen, oxygen, He, hydrogen, fluorine, or carbon is used, it is moredifficult to achieve bonding only by contacting as compared to wheninert gas (Ar, etc.) is used, and bonding can be achieved at lowtemperature.

In the bonding method and the bonding apparatus, the gas may be theatmospheric air. In the case of the atmospheric air, handling is easyand the above-described effect can be expected.

Regarding a method of cleaning an object to be bonded using an energywave, a plasma, which requires about 10⁻² Torr, is easy and effective,as compared to an atom beam and an ion beam, which require a high vacuumof about 10⁻⁵ Torr. Also, when Ar is used as reaction gas, etching isefficiently performed, and since Ar gas is inert, reaction matter is notformed on the surface of the object to be bonded.

One of the objects to be bonded may be a light emitting element, a probefrom a power supply may be contacted with the bonding portionfunctioning as an electrode of the light emitting element, a lightemitting point of the light emitting element may be recognized using arecognizing means to adjust the position of the light emitting elementto an optimum position while the light emitting element is caused toelectrically function, and thereafter, the objects to be bonded may bebonded together in a solid phase at room temperature.

In the bonding method and the bonding apparatus, the light emittingelement may be of a surface light emission type, or may be of a type inwhich light is emitted in a direction perpendicular to the bondingsurface of the light emitting element and toward one of the objects tobe bonded.

In the bonding method and the bonding apparatus, one of the objects tobe bonded may be a light emitting element which emits light parallel tothe bonding surface, and one probe may be contacted with an electrodeopposed to the bonding surface of the light emitting element, and theother probe may be contacted with the other electrode, so that the lightemitting element is caused to electrically function, and the lightemitting point may be recognized using a recognizing means, and theposition of the light emitting element may be adjusted to an optimumvalue, and thereafter, metal bonding may be performed in a solid phaseby heating at 180° C. or less. Particularly, when the functional deviceis a light emitting element, the positioning of the light emitting pointand an optical fiber requires accuracy of the order of submicrons, andthe present invention is effective in terms of accuracy. Also, in thecase of the light emitting element, heat radiation occurs during lightemission, so that reliability is required at a high temperature of 250°C. or more. Therefore, the bonding method of the present invention iseffective in which bonding is performed at low temperature andreliability can be maintained at temperature higher than the bondingtemperature.

In the present invention, as illustrated in FIGS. 12 and 13, when thelight emitting element is, for example, a laser diode which emits lightparallel to the bonding surface, the present invention is effective. Inthis case, as illustrated in FIGS. 12 and 13, an electrode which is thebonding surface of the light emitting element is provided facing theobject to be bonded, and the position is adjusted by moving verticallywhile holding the opposite surface. While pressing the lower electrodeof the light emitting element against the upper electrode of the objectto be bonded, the electrode on the holding surface of the light emittingelement is contacted with the upper electrode of the object to bebonded, so that the light emitting element is caused to electricallyfunction. After the light emitting point is adjusted to an optimumposition, metal bonding is performed in a solid phase by heating at 180°C. or less.

In the bonding method and the bonding apparatus, the light emittingelement may be a surface light emission type, and a type in which lightis emitted in a direction perpendicular to the bonding surface andtoward one object to be bonded. The bonding electrode of the object tobe bonded may be contacted with the bonding surface (electrode) on thesurface of the light emitting element, and probing may be performed withrespect to the other end of the object to be bonded to cause the lightemitting element to electrically function to recognize the lightemitting point using a recognizing means, and after the position of thelight emitting element is adjusted to an optimum value, metal bondingmay be performed in a solid phase by heating at 180° C. or less. Asdescribed above, when the light emitting element (surface light emittinglaser, etc.) which emits light in a direction perpendicular to thebonding surface is used instead of the light emitting element (FIG. 13)which emits light parallel to the bonding surface, a simpleconfiguration can be particularly obtained since the light emittingdirection and the electrode direction can be provided on the lower sideas illustrated in FIG. 14. In this case, as illustrated in FIG. 14, theposition is adjusted while the light emission surface is placed facingthe object to be bonded and the opposite surface is held. Since theelectrode is positioned on the same side as that of the light emissionsurface, a probe is contacted with the electrode on the upper surface ofthe object to be bonded while pressing against the electrode of theobject to be bonded, to cause the light emitting element to electricallyfunction. After adjusting the light emitting point to an optimumposition, metal bonding is performed in a solid phase by heating at 180°C. or less. When an optical fiber is not buried and emits lightdownward, light can be recognized from the side by providing an opticalpath converting means comprising a prism to the stage, for example.

In the bonding method and the bonding apparatus, regarding the method ofadjustment to an optimum value, light emitted from the light emittingelement may be input to an optical fiber, and the input value may bedetected so as to adjust the position of the light emitting element.Regarding the method of recognizing the light emitting point, when lightis input to the optical fiber, the other end of the optical fiber isconnected to a measuring apparatus, and the output is monitored toadjust a center position which provides a maximum value. This is aneffective and easy method. Regarding a method of recognizing a lightemitting point, a position which provides a maximum light amount isgenerally considered as the light emitting point, or alternatively,preferably a light emitting point is recognized, taking intoconsideration a contrast state therearound as well as a maximum value,even though the light emitting point may not have the maximum value.

In the bonding method and the bonding apparatus, an object-to-be-bondedrecognizing means and a light emitting point recognizing means may beprovided, and the method of adjustment to an optimum value may comprisea first step of recognizing the position of an object to be bonded usingthe object-to-be-bonded recognizing means, a second step of readinglight emitted from the light emitting element using a matrix imagingelement to recognize the position of the light emitting point, and athird step of adjusting the position of the light emitting element basedon the result of the recognition. Particularly, when light is not inputto an optical fiber, or the other end of the optical fiber is notconnected, the position of the object to be bonded is initiallyrecognized using the object-to-be-bonded recognizing means to recognizea position where the light emitting point is to be placed. Next, thelight emitting point is directly input to the matrix imaging element todetect the input value, and the position of the light emitting elementis adjusted so that the position on the matrix imaging element whichprovides a maximum light amount matches a target position on the matriximaging element. Specifically, initially, the light emitting element iscaused to emit light, and the light is read using the matrix imagingelement, so that the maximum light amount position on the matrix imagingelement is obtained. The position of the matrix imaging element attachedon a table in a manner which allows the matrix imaging element to moveis previously known, so that the light emitting point position of thelight emitting element can be recognized. Therefore, the position of alight emitting point which is to be placed on the matrix imaging elementis originally known, and therefore, the position of the light emittingpoint is corrected so that the light emitting element is placed at aposition on the matrix imaging element which allows the maximum lightamount. Regarding a method of recognizing the light emitting point usinga matrix imaging means, a position which provides a maximum light amountis generally considered as the light emitting point, or alternatively,preferably the light emitting point is recognized in units of a subpixelof the imaging element, taking into consideration a contrast statetherearound as well as a maximum value, even though the light emittingpoint may not have the maximum value.

In the bonding method and the bonding apparatus, the object-to-be-bondedrecognizing means and the light emitting point recognizing means may beseparate matrix imaging elements, and relative positions of the imagingelements may be recognized using a reference jig which determinespositions of a light emitting point and a mark position of an object tobe bonded mark, thereby performing calibration and recognition. Forexample, when the light emitting point recognizing means and theobject-to-be-bonded recognizing means have different optical systemmagnifications, separated matrix imaging elements are provided. In thiscase, assuming that relative positions of the separate matrix imagingelements are not known, even if the mark of an object to be bonded isrecognized, it cannot be determined where to place the light emittingpoint. Therefore, if the relative positions of the light emitting pointand the mark for recognizing the object to be bonded are recognizedusing a reference jig which previously determines the relativepositions, the relative position relationship can be calibrated.Thereby, it is possible to recognize a light emitting point and anobject to be recognized on an object to be bonded even when they havedifferent sizes.

In the bonding method and the bonding apparatus, when the light emittingelement is caused to electrically function and the position of the lightemitting point is recognized using the recognizing means, light may beintermittently emitted so as to recognize the position. In the case ofthe light emitting element, if light is continuously emitted since heatis radiated during light emission, heat is accumulated to about 250° C.In this case, bonding is performed during position adjustment, and aposition error occurs due to thermal expansion or the like. Therefore,by emitting light intermittently, and instantaneously capturing thelight emitting point in synchronization with light emission, heataccumulation can be prevented and the light emitting point can berecognized at low temperature.

In the bonding method and the bonding apparatus, an alignment mark maybe provided on both the objects to be bonded, an alignment markrecognizing means may be provided, and after the positions of both theobjects to be bonded are corrected using the alignment marks, theobjects to be bonded may be caused to electrically function so as to beadjusted to an optimum position. In the case where the light emittingpoint is recognized, when the position accuracy is initially poor, ittakes a long time to align the center of the light emitting point bycontacting the light emitting element if a position error is large.Also, since the light emitting point recognizing means needs to have alarge visual field, the accuracy is also poor. Therefore, preferably,the alignment marks previously provided on the light emitting elementand the object to be bonded are used to recognize both the alignmentmarks using a recognizing means, and the position is corrected toperform rough positioning before recognizing the light emitting point.If an outer shape, a recognizable pattern, or the like is provided, itcan be recognized as an alignment mark without particularly providing analignment mark.

In the bonding method and the bonding apparatus, the light emittingpoint recognizing means and the object-to-be-bonded recognizing meansmay be composed of the same recognizing means. In the bonding method andthe bonding apparatus, at least one of the objects to be bonded may beheld using a tool having an optical path converting means, and theobject to be bonded and the light emitting point may be recognized fromthe side. In the case of a surface light emitting element, if an objectto be bonded is held using a tool having an optical path convertingmeans, such as a prism or a mirror, and optical path conversion isperformed from the bottom to the side, both the position of the objectto be bonded and the position of the light emitting point can be readfrom the side, resulting in a simple structure. In the case of aparallel light emitting element, the light emitting element is heldusing a tool having an optical path converting means, and an uppersurface mark on the object to be bonded can be read from the side,resulting in a simple structure. The position of an object to be bondedis determined by image-recognizing an alignment mark on a light emittingelement or a substrate, or an outer shape thereof, and is used so as torecognize a mark on a substrate to determine the position of the lightemitting point or so as to recognize alignment marks on the lightemitting element and the substrate to previously perform alignment.

If IR (infrared) light is used, at least one of the objects to be bondedis caused to be transparent and alignment marks on the objects to bebonded can be read. For example, in the case of a light emitting elementwhich emits light parallel to the bonding surface, an optical pathconverting means is provided in the light emitting element holding tool,the light emitting element or the object to be bonded is caused to betransparent so that alignment marks can be read by recognizing IR light.Regarding an IR light source, reflected light may be used on the sameaxis, or a light source may be used on the opposite side and transmittedlight may be used. The optical path converting means may be provided onthe object-to-be-bonded holding stage instead of the holding tool. Ifthe object-to-be-bonded position recognition including the lightemitting point and the light emitting element is recognized in the samedirection using the same recognizing means by using the optical pathconverting means, measurement can be performed with higher accuracy. Forexample, if an optical system of the light emitting point recognizingmeans is used to recognize the mark on or an outer shape of the objectto be bonded, a position at which the next light emitting point to beplaced is easily known after the recognition of the object to be bonded,so that, preferably, a relative position error caused by the recognizingmeans being provided separately, a change over time due to thermalexpansion, or the like, does not occur. Also, the apparatus can besimplified, and particularly it is not necessary to provide a multiaxialmoving table in the recognizing means, so that the apparatus can besimplified, and the apparatus can be further simplified if the alignmenttable is limited to only either of the head or the stage. Even ifseparate matrix imaging elements are provided, an integrated structurecan be obtained by splitting the optical system partway.

In a light emitting module fabricated using the above-described bondingmethod, a light emitting element is efficiently mounted with highaccuracy using the above-described method, so that the light emittingmodule can be fabricated with high accuracy and low cost, i.e., thepresent invention is effective.

In the bonding method, one of the objects to be bonded may be a chip,and the other object to be bonded may be a wafer on which a plurality ofthe chips are to be mounted, and a plurality of the chips may becontinuously bonded to the wafer.

In the bonding apparatus, one of the objects to be bonded may be a chip,and the other object to be bonded may be a wafer on which a plurality ofthe chips are to be mounted, and a plurality of the chips may becontinuously bonded to the wafer.

As illustrated in FIG. 7, room-temperature bonding can be achieved bypressing even in the atmospheric air if the object to be bonded is notallowed to stand after dry cleaning (surface activation using an energywave). This may be because, although a thin attached layer is formed onthe bonding surface (bonding portion), the layer is so thin that it canbe crushed by pressing. Since solder is heated at high temperature so asto mount a plurality of chips onto a wafer, surrounding solder on thewafer is also affected, and may be defectively melted or oxidized, or abonded chip may be defectively displaced since solder is melted. In thepresent invention, bonding can be performed at no more than 183° C.which is the melting point of solder, so that there is not an influenceon surroundings, and mounting can be continuously performed. Also, sincebonding can be performed in a solid phase, the above-described positionerror due to melting does not occur. Note that a chip which had not beensubjected to an energy wave treatment was not bonded. Note that the chipgenerally indicates a piece obtained by dicing a wafer, includingmounted parts, such as a transistor, a resistance, a capacitor, areactance, and the like.

In the bonding method and the bonding apparatus, a time required to bonda chip and a wafer may be two seconds or less, and chips may becontinuously mounted. In the case of solder, after heating for melting,if a chip is released by the time when the solder is cooled and fixed, aposition error occurs or the solder is displaced, so that it takes along time to continuously mount chips, resulting in poor productionefficiency. For example, a time required to bond one chip is about 10seconds. However, in the present invention, since bonding is achievedonly by pressing, the bonding time can be extremely short. Thus, ifchips are continuously bonded onto a wafer where the bonding time is twoseconds or less, the efficiency is good. Preferably, the bonding time isone second or less. More preferably, the bonding time is 0.5 seconds orless, since it is shorter than when ultrasonic vibration bonding isperformed.

During the time when the chips are continuously bonded to the wafer,after a predetermined time has passed, the wafer may be treated againwith the energy wave, and thereafter, bonding of the chips to the wafermay be resumed. Assuming that a plurality of chips are bonded onto asingle wafer, if the number of chips is large, it takes a long time. Inorder to achieve room-temperature bonding in the atmospheric air,bonding is performed within about one hour after dry cleaning (anactivation treatment using an energy wave). This is because, ifotherwise, adhering substances increases on a bonding surface of anobject to be boded, so that bonding cannot be performed. Therefore, drycleaning is preferably performed again using an energy wave (alow-pressure plasma, etc.) within one hour, preferably 30 minutes.Therefore, a cleaning machine (energy wave emitting means) is coupledwith the bonding apparatus for the objects to be bonded so that, when achip is bonded onto a wafer, after a predetermined time has passed, thewafer is temporarily transported to the cleaning machine, in whichcleaning is in turn performed again. After cleaning, the wafer is set onthe stage again to start chip bonding. Thereby, a number of chips can becontinuously bonded to a wafer in the atmospheric air at roomtemperature.

In a semiconductor, since a number of electrodes are bonded using bumps,damage occurs at high temperature, and therefore, low-temperaturebonding is desired. When bonding is performed using bumps having a finepitch smaller than about 50 μm, low-temperature bonding which suppressesthermal expansion is desired. In view of damage to a circuit surface, alow load is required. If chips are continuously bonded to a wafer, theefficiency is good. For these reasons, the present invention ispreferable.

The object to be bonded may be a chip or a wafer composed of asemiconductor or a MEMS device.

A device which is formed with the bonding method, wherein the device isa semiconductor device, a MEMS device, or the like.

Flipchip bonding for a semiconductor chip which has a number ofelectrode portions (metal convex portions) is expected to providemounting having a high accuracy ranging from minute pitch electrodes toseveral micrometers or less, and is desired to be performed at a lowtemperature of 180° C. or less, preferably room temperature, because ofan influence of heat to a semiconductor. Therefore, this embodiment isparticularly effective to the flipchip bonding.

In the bonding method and the bonding apparatus, a metal protrusion maybe provided on at least one of objects to be bonded, and at least one ofthe objects to be bonded may be a semiconductor chip. A semiconductorapparatus may be fabricated by the method in which a metal protrusion isprovided on at least one of objects to be bonded, and at least one ofthe objects to be bonded is a semiconductor chip. Flipchip bonding for asemiconductor chip which has a number of electrode portions (metalconvex portions) is expected to provide mounting having a high accuracyranging from minute pitch electrodes to several micrometers or less, andis desired to be performed at a low temperature of 180° C. or less,preferably room temperature, because of an influence of heat to asemiconductor. Therefore, this embodiment is particularly effective tothe flipchip bonding.

By attaching semiconductors, a three-dimensional structure can bepreferably obtained, resulting a semiconductor apparatus having a higherpackaging density. Preferably, after wafers are bonded together, thewafers are diced into chips, thereby increasing the productionefficiency.

EFFECTS OF THE INVENTION

In a bonding method of bonding a plurality of objects to be bondedhaving a metal bonding surface at low temperature, room-temperaturebonding can be performed in the atmospheric air. Direct bonding can beobtained without a high profile irregularity which is required byconventional room-temperature bonding.

At least one of the objects to be bonded may be a semiconductor, and thebonding surface of each of the objects to be bonded may be subjected toplasma cleaning using the low-pressure plasma which is generated withelectric field having alternating + and − directions generated by analternating power supply before the cleaned bonding surfaces are bondedtogether in a solid phase at room temperature. Thereby, the + ion andthe − electron can be caused to alternately strike the object to bebonded so as to neutralize before accumulating charge. Thereby, it ispossible to avoid charge-up damage. By adjusting the times of the +region and the − region using a bias voltage Vdc or the pulse width ofpulsed waves, an optimum region for neutralization can be created.

In the bonding method of bonding a plurality of objects to be bondedhaving a metal bonding surface formed of gold or copper at lowtemperature, room-temperature bonding can be performed in theatmospheric air. Also, a bonding load can be reduced.

In a chamber having a reduced pressure, both objects to be bonded areshifted to side positions so that the bonding surfaces do not overlapeach other, and after both the bonding surfaces are subjected to plasmacleaning, the objects to be bonded are shifted to positions which allowboth the bonding surfaces to face each other, and at least one of theobjects to be bonded is shifted in a direction substantiallyperpendicular to the bonding surface of the object to be bonded,followed bonding. Thereby, it is possible to clean the objects to bebonded using a plasma (surface activating treatment) while preventingorganic substances or the like from readhering to the other object to bebonded. Also, a gap in height direction between both the objects to bebonded can be minimized, thereby making it possible to perform bondingwithout a position error after alignment and with high accuracy.

A contour-shaped bonding portion is formed in at least one space betweenthe device and the object to be bonded serving as a lid using a bondingmetal, and bonding portions of the device and the object to be bondedare subjected to surface activation using an energy wave (e.g., an atombeam, an ion beam, or a plasma) in a reduced pressure chamber, andthereafter, the bonding portions are bonded at a low temperature of 180°C. or less, thereby making it possible to enclose a predeterminedatmosphere in a space between the device and the object to be bonded.Thus, an atmosphere can be enclosed using a single apparatus and asingle step, resulting in a reduction in cost and an increase inproductivity. Also, an evacuation hole or a resin sealing material isnot required. Since bonding can be achieved at low temperature, thepresent invention can be applied to a device susceptible to heat, or adevice in which distortion occurs due to thermal expansion caused by acombination of different materials and which cannot endurehigh-temperature bonding.

Direct bonding can be performed at a position which is adjusted while afunctional device is caused to function, resulting in high-efficiencybonding without a position error. Since bonding can be performed at lowtemperature and in a solid phase, bonding can be achieved with highaccuracy.

In a bonding method of bonding a plurality of objects to be bondedhaving a metal bonding surface formed of gold or copper at lowtemperature, room-temperature bonding can be performed in theatmospheric air in a solid phase. Also, chips can be continuouslymounted onto a wafer with a short bonding time and high efficiency.Also, bonding can be performed using a low load even at room temperaturein a solid phase.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a relationship between metal hardnessand bonding strength.

FIGS. 2A and 2B are schematic diagrams illustrating how an attached filmis removed by irregularities on a bonding interface.

FIGS. 3A and 3B are schematic diagrams illustrating rotation of crystalorientation on a bonding interface during bonding.

FIG. 4 is a diagram illustrating a relationship between bonding surfaceroughness and bonding strength.

FIG. 5 is a diagram illustrating a relationship between a head stop timeduring bonding and bonding strength.

FIG. 6 is a diagram illustrating a relationship between heatingtemperature during bonding when a head is stopped, and bonding strength.

FIG. 7 is a diagram illustrating a relationship between a bonding loadin the presence or absence of leveling, and bonding strength.

FIG. 8 is a schematic diagram illustrating bump surface roughness.

FIG. 9 is a schematic diagram illustrating a variation in bump height.

FIG. 10 is a schematic diagram of leveling.

FIG. 11 is a schematic diagram illustrating bonding between a chip and asubstrate after leveling.

FIG. 12 is a diagram for explaining a center aligning method for a lightemitting element.

FIG. 13 is a side view of a method for aligning the center of a sidelight emitting element to an optical fiber on a PLC.

FIG. 14 is a side view of a method for aligning the center of a sidelight emitting element to an optical fiber-buried substrate.

FIG. 15 is a light emitting element center aligning bonding apparatus.

FIGS. 16A and 16B are schematic diagrams illustrating diffusion of agold film.

FIG. 17 is a diagram illustrating a configuration for simultaneousrecognition using an optical path converting means of a parallel lightemitting element, as viewed from the side.

FIG. 18 is a diagram illustrating a configuration for simultaneousrecognition using an optical path converting means of a surface lightemitting element, as viewed from the side.

FIG. 19 is a diagram illustrating a bonding apparatus.

FIG. 20 is a diagram illustrating a bonding apparatus.

FIGS. 21A to 21G are diagrams illustrating a bonding process.

FIG. 22 is a diagram illustrating an alignment in the atmospheric airusing a two-side recognizing means.

FIG. 23 is a diagram illustrating an alignment in the vacuum atmosphereusing an IR recognizing means.

FIG. 24 is a diagram illustrating a configuration of a device at a chiplevel.

FIG. 25 is a diagram illustrating a configuration of a device at a waferlevel.

FIG. 26 is a diagram illustrating an RF plasma power supply.

FIG. 27 is a diagram illustrating a pulsed wave plasma power supply.

FIG. 28 is a method for reducing damage, depending on a pulse width.

FIG. 29 is a diagram illustrating a bonding apparatus.

FIG. 30 is a diagram illustrating a cleaning apparatus and a bondingapparatus.

FIG. 31 is a diagram illustrating a bonding apparatus.

FIGS. 32A to 32K are diagrams illustrating a bonding process.

DESCRIPTION OF REFERENCE CHARACTERS

20 . . . chip (object to be bonded)

20 a . . . bump (bonding portion)

22 . . . chip (object to be bonded)

22 a . . . bump (bonding portion)

25 . . . vertical drive mechanism

26 . . . head section

28 . . . mounting mechanism (stage)

42,44 . . . probe

531 . . . Z axis (vertical drive mechanism)

532 . . . piston type head (head)

539 . . . lower electrode (stage)

550 . . . copying mechanism (spherical bearing)

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

Hereinafter, a first embodiment of the present invention will bedescribed with reference to the drawings. FIG. 15 illustrates the firstembodiment of a bonding apparatus according to the present invention. Inthis embodiment, an apparatus for bonding a chip 20 formed of asemiconductor (first object to be bonded) and a substrate 22 (secondobject to be bonded) will be described as an example. A bonding surfaceof the chip 20 has a metal electrode 20 a which is an electrode and isformed of gold, and a bonding surface of the substrate 22 has a metalelectrode 22 a which is an electrode and is provided at a position whichallows to face the metal electrode 20 a of the chip. The metal electrode20 a of the chip and the metal electrode 22 a of the substrate arebonded together by pressing.

The bonding apparatus roughly includes a bonding mechanism 27 includinga vertical drive mechanism 25 and a head section 26, a mountingmechanism 28 including a stage 10 and a stage table 12, a positionrecognizing section 29, a transport section 30, and a control apparatus31. The vertical drive mechanism 25 moves the head section 26 verticallyusing a vertical drive motor 1 and a bolt-nut mechanism 2 while beingguided by a vertical guide 3. The head section 26 is guided verticallyby a head escape guide 5, and contacts a pressing force detecting means32 for detecting a pressing force and the vertical drive mechanism 25while being pulled by a head own-weight counter 4 for canceling thehead's own weight and pressing the head against the pressing forcedetecting means 32.

The head section 26 is composed of a chip holding tool 8 which sucks andholds the chip 20, a tip tool 9, a head's alignment table 7 which hasmovement axes of translation and rotation and performs positioncorrection, and a head holding section 6 which supports them. A heatingheater is buried and provided inside the chip holding tool 8. Themounting mechanism 28 is composed of the stage 10 which sucks and holdsthe substrate 22, and the stage table 12 which has movement axes oftranslation and rotation and performs alignment of positions of a chipand a substrate. A stage heater 11 is included in the stage 10. Thebonding mechanism is coupled with a frame 34 and is linked to a pedestal35 via four supporting poles 13 provided around a pressing center.

The position recognizing section 29 is composed of a vertical markrecognizing means 14 which is inserted between a chip and a substratefacing each other and recognizes alignment marks for recognizingpositions of the chip (upper position) and the substrate (lowerposition), and a recognizing means moving table 15 which moves thevertical mark recognizing means 14 horizontally and/or vertically. Thetransport section 30 includes a substrate transport apparatus 16 and asubstrate transport conveyer 17 which transport the substrate 22, and achip supply apparatus 18 and a chip tray 19 which transport the chip 20.A control section 31 includes a control of the whole apparatus and anoperation section. Particularly in a pressing force control, the controlsection 31 controls the torque of the vertical drive motor 1 based on asignal from the pressing force detecting means 32 to control a pressingforce for bonding.

Next, a series of operations will be described. The chip 20 is suppliedfrom the chip tray 19 to the chip holding tool 8 by the chip supplyapparatus 18, and is sucked and held by the chip holding tool 8. Thesubstrate 22 is supplied from the substrate transport conveyer 17 to thestage 10 by the substrate transport apparatus 16, and is sucked and heldby the stage 10. The vertical mark recognizing means 14 is insertedbetween the chip 20 and the substrate 22 whose bonding surfaces faceeach other by the recognizing means moving table 15. Positions of thepositioning alignment marks of the chip 20 and the substrate 22 facingeach other are recognized by the vertical mark recognizing means 14.Using the chip 20 as a reference, the position of the substrate 22 ismoved in a translation direction and a rotation direction by the stagetable 12 for the purpose of alignment. During alignment, positioncorrection may be performed by the stage table 12 and the head'salignment table, or only by the head's alignment table. Only either ofthem may be provided.

When bonding positions of the chip 20 and the substrate 22 match eachother, the vertical mark recognizing means 14 is retreated by therecognizing means moving table 15. Next, the head section 26 is loweredby the vertical drive mechanism 25 so that the chip 20 and the substrate22 contact each other. A position in a height direction of the headsection 26 is detected by a head height detecting means 24. Contacttiming of the chip 20 and the substrate 22 is detected by the pressingforce detecting means 32, and the vertical drive motor is switched froma position control to a torque control. The head height is alsomonitored by the head height detecting means 24 during the time whenpressing is performed in the torque control, so that the position in theheight direction can be controlled. After completion of bonding, thesuction of the chip 20 is released, so that the chip 20 is left on thestage while being mounted on the substrate 22. The substrate 22 isdischarged to the substrate transport conveyer 17 by the substratetransport apparatus 16. The series of operations are ended.

In order to performing metal bonding while keeping a solid phase at alow temperature of 180° C. or less in the atmospheric air, the bondingsurfaces (portions to be bonded) of objects to be bonded which areformed of a metal (the chip 20, the substrate 22) are previously etched(cleaned) by several nanometers in a vacuum using an energy wave (anatom beam, an ion beam, or a plasma) to remove adhering substances. Whenbonding is performed in the atmospheric air after cleaning (surfaceactivating treatment), an adhering substance layer is formed on abonding surface, so that bonding is not achieved only by contacting.However, since the adhering substance layer is thin immediately aftercleaning, the adhering substance layer is crushed by pressing, so thatthe crushed adhering substance layer forms a new surface which allowsbonding. In this embodiment, gold is used as a bonding portion, whichhas a Vickers hardness of 60 Hv, so that the chip 20 and the substrate22 are firmly bonded together even at room temperature (see FIG. 1).

Second Embodiment

Next, a second embodiment of the bonding apparatus of the presentinvention will be described in detail with reference to FIGS. 16A and16B. This embodiment is significantly different from the above-describedfirst embodiment in that a bonding portion of an object to be bonded isconstructed by forming a gold film on a surface of a base materialformed of a metal, and other parts of this embodiment are similar tothose of the first embodiment. Hereinafter, the second embodiment willbe described in detail, mainly in terms of the difference from the firstembodiment. Note that the same configuration and operation as those ofthe first embodiment will not be described.

In the second embodiment, bonding portions of the chip 20 and thesubstrate 22 are formed as metal bumps as follows. Specifically, aplurality of coppers are used as base materials 20 b and 22 b, and goldfilms 20 c and 22 c are formed on surfaces of the base materials 20 band 22 b. The metal bumps are subjected to a surface activatingtreatment using an energy wave, and thereafter, are bonded together inthe atmospheric air, followed by low-temperature heating to diffusegold. FIG. 16A illustrates the bonding portion composed of the copperbase material and the gold film. FIG. 16B illustrates how the gold films20 c and 22 c are diffused in the base materials 20 b and 22 b bylow-temperature heating after the objects to be bonded (FIG. 16A) arebonded together. Note that, if the bonding surface is formed of gold, itis difficult for organic substances or the like to readhere to thebonding surface after the surface activating treatment, and bonding canbe achieved in the atmospheric air if it is performed within severalhours after the surface activating treatment. Thus, if the gold film isdiffused into the base material after room-temperature bonding, the basematerials are bonded together after bonding, resulting in a highstrength and a uniform material structure. Regarding the diffusionmethod, diffusion can be achieved by allowing the bonded objects tostand at room temperature. Alternatively, diffusion can be acceleratedby heating at low temperature. In this embodiment, by heating at 150° C.for two hours, the gold films 20 c and 22 c were able to be diffusedinto the base materials 20 b and 22 b.

When an object to be bonded is an electronically functioning device in asemiconductor or a MEMS device, a conventional Al electrode is desiredto be changed to a copper electrode in terms of a current-carryingcapacity. However, it is practically difficult to use a copper bumpbecause its bonding temperature is high. Therefore, as in thisembodiment, the bonding temperature can be reduced by covering thesurface of a copper base material with a gold film, the reduced bondingtemperature is effective. In addition, it is effective that atmospheres,such as gas, the atmospheric air, and the like, can be selected inaddition to a vacuum. Thereafter, if the gold is diffused into the basematerial, the coppers are bonded together, so that the object isachieved.

Third Embodiment

Next, a third embodiment of the bonding apparatus of the presentinvention will be described in detail. This embodiment is significantlydifferent from the above-described first and second embodiments in thatminute irregularities are formed on a surface of a bonding portion, andother parts and operations of this embodiment are similar to those ofthe first and second embodiments, and will not be described.Hereinafter, specific features of this embodiment will be described indetail.

According to this embodiment, the convex portions are crushed bypressing when objects to be bonded are bonded as illustrated in FIGS. 2Aand 2B and are then caused to be spread, so that a new surface appearsand bonding is achieved. When viewed microscopically, crystalorientations arranged as illustrated in FIGS. 3A and 3B are rotated bythe convex portion being crushed, so that the new surface appears. Ascan be seen from FIG. 4, when the surface roughness (minuteirregularities) is 120 nm or more, a sufficient bonding strength isobtained.

In the case where surfaces are bonded together, even when a plurality ofconvex-shaped bonding portions are used so as to cause the microirregularities to be effective as described above, the bonding area issmaller than that of surface bonding, but a similar effect is obtained.In order to crush the micro irregularities to achieve bonding, thebonding metal needs to have a low hardness. In this embodiment, sincegold, which has a hardness of 200 Hv or less, was used as a bondingportion, firm bonding was able to be achieved. Note that, when copper orAl was used for a bonding portion, bonding was able to be effectivelyachieved. In this case, when the pressing force was 150 MPa or more,firmer bonding was able to be achieved. Particularly, when a bondingportion was formed of gold, a low hardness was obtained and oxidationdid not occur even in the atmospheric air.

When Ar plasma is used to clean a bonding portion (surface activatingtreatment), a rough bonding surface is obtained by setting a cleaningtime to be longer (e.g., three minutes, where an ordinary time is 30seconds). When Ar plasma is used to clean an object to be bonded forjust a time which allows the roughness to be 120 nm or more, a surfaceactivating treatment, and a process for forming minute irregularities onthe surface of a bonding portion can be simultaneously performed,resulting in high efficiency.

Fourth Embodiment

Next, a fourth embodiment will be described in detail. Hereinafter, adifference between the fourth embodiment and the above-described firstto third embodiments will be described. The same parts and operations asthose of the first to third embodiments will not be described.

In the above-described third embodiment, when a pressing force isinstantaneously applied to an object to be bonded, irregularities of abonding surface (bonding portion) are elastically deformed, so thatcrystal at an interface may not be rotated. Also, the elasticdeformation remains as residual stress which acts in a direction whichcauses the bonding portion to peel off, rather than bonding force,resulting in a reduction in bonding strength. As a method for preventingthis, the head height of the head section 26 is kept constant for apredetermined time, so that the crystal cannot resist a load at thebonding interface of the objects to be bonded as viewed microscopically,and therefore, crystal orientations are rotated or particles are moved.As a result, a new surface appears and performs bonding, and themovement of particles removes the residual stress. The effect wasobtained when the stop time was one second or more, depending on thematerial or the bonded state, and a change was not observed when thestop time was two minutes or more, as illustrated in FIG. 5.

In addition, when heating is performed at 180° C. or less during thestop time, the rotation of crystal orientations or the movement ofparticles is efficiently performed, so that bonding is developed andresidual stress is removed, resulting in an increase in bondingstrength. As the heating temperature, 180° C. or less was sufficient(low-temperature heating). Flipchip bonding for a semiconductor chipwhich has a number of electrode portions (metal convex portions) isexpected to provide mounting having a high accuracy ranging from minutepitch electrodes to several micrometers or less, and is desired to beperformed at a low temperature of 180° C. or less, preferably roomtemperature, because of an influence of heat to the semiconductor.Therefore, this embodiment is particularly effective to the flipchipbonding.

Although the embodiment for a chip and a substrate has been described asan embodiment, an object to be bonded may be formed of other materialsin addition to semiconductors. Although gold, Al, copper, and the likeare suitable for the bonding portion, other metals or materials otherthan metals may be used as long as they can achieve surface activationbonding.

The semiconductor chip may be in any form, such as a chip, a wafer, orthe like. The metal protrusion may be a plurality of shapes separatelyprovided or a shape in which a certain continuous region is confined.The entire surface may be a bonding surface.

Fifth Embodiment

Next, a fifth embodiment of the present invention will be described indetail. This embodiment is significantly different from theabove-described first to fourth embodiments in that the chip 20 is alight emitting element. Hereinafter, specific features of thisembodiment will be described in detail. FIG. 12 is a diagram forexplaining a method for aligning centers of a side-surface lightemitting element and a PLC (Planner Light wave guide Circuit) substratehaving a V-groove for fixing a fiber, and FIG. 13 is a side viewthereof. In this embodiment, an apparatus for aligning centers of alight emitting element 20 (a first object to be bonded, a functionaldevice) and a substrate 22 (a second object to be bonded) and bondingthem will be described as an example. A metal electrode which is anelectrode and is formed of gold is provided on a bonding surface of thelight emitting element 20, and a metal electrode which is an electrodeis provided on a bonding surface of the substrate 22 and at a positionwhich allows to face the metal electrode of the light emitting element.The metal electrode of the light emitting element and the metalelectrode of the substrate are bonded together by heating after centerpositions of a light emitting point 41 and an optical fiber 46 arealigned.

Next, a bonding apparatus of this embodiment will be described indetail, focusing on a difference between this embodiment and theabove-described embodiments. The bonding apparatus roughly includes abonding mechanism 27 including a vertical drive mechanism 25 and a headsection 26, a mounting mechanism 28 including a stage 10 and a stagetable 12, a position recognizing section 29, a transport section 30, anda control apparatus 31. The vertical drive mechanism 25 moves the headsection 26 vertically using a vertical drive motor 1 and a bolt-nutmechanism 2 while being guided by a vertical guide 3. The head section26 is guided vertically by a head escape guide 5, and contacts apressing force detecting means 32 for detecting a pressing force and thevertical drive mechanism while being pulled by a head own-weight counter4 for canceling the head's own weight and pressing the head against thepressing force detecting means 32. The head section 26 is composed of achip holding tool 8 which sucks and holds the light emitting element 20,a tip tool 9, a head's alignment table 7 which has movement axes oftranslation and rotation and performs position correction, and a headholding section 6 which supports them. A heating heater is buried andprovided inside the chip holding tool. The mounting mechanism 28 iscomposed of a stage 10 which sucks and holds the substrate 22, and astage table 12 which has movement axes of translation and rotation andperforms alignment of positions of a light emitting element and asubstrate. A stage heater 11 is included in the stage 10. The bondingmechanism is coupled with a frame 34 and is linked to a pedestal 35 viafour supporting poles 13 provided around a pressing center. The positionrecognizing section 29 is composed of a vertical mark recognizing means14 which is inserted between a light emitting element and a substratefacing each other and recognizes alignment marks for recognizingpositions of the light emitting element (upper position) and thesubstrate (lower position), and a recognizing means moving table 15which moves the vertical mark recognizing means 14 horizontally and/orvertically. A light emitting point recognizing means 33 is provided at atip of the vertical mark recognizing means 14, is shifted to anarbitrary position by the recognizing means moving table 15, and iscapable of measuring a position of a light emitting point.

Assuming that the optical fiber is buried in the substrate and an end ofthe optical fiber is extending outside, if the end is input directlyinto a photometer, a maximum point (light emitting point) can bedetected without using the light emitting point recognizing means. Thetransport section 30 includes a substrate transport apparatus 16 and asubstrate transport conveyer 17 which transport the substrate 22, and alight emitting element (chip) supply apparatus 18 and a light emittingelement (chip) tray 19 which transport the light emitting element 20. Acontrol section 31 includes a control of the whole apparatus and anoperation section. Particularly in a pressing force control, the controlsection 31 controls the torque of the vertical drive motor 1 based on asignal from the pressing force detecting means 32 to control a pressingforce for bonding.

Next, a series of operations will be described. The light emittingelement 20 is supplied from the light emitting element tray 19 to thelight emitting element holding tool 8 by the light emitting elementsupply apparatus 18, and is sucked and held by the light emittingelement holding tool 8. The substrate 22 is supplied from the substratetransport conveyer 17 to the stage 10 by the substrate transportapparatus 16, and is sucked and held by the stage 10. The vertical markrecognizing means 14 is inserted between the light emitting element 20and the substrate 22 whose bonding surfaces face each other by therecognizing means moving table 15. Positions of the positioningalignment marks of the light emitting element 20 and the substrate 22facing each other are recognized by the vertical mark recognizing means14. Using the light emitting element 20 as a reference, the position ofthe substrate 22 is moved in a translation direction and a rotationdirection by the stage table 12 for the purpose of alignment. Positioncorrection may be performed with respect to the light emitting elementby the head's alignment table. In this example, the head's alignmenttable is assumed to be an alignment table which is composed of ahigh-accuracy piezo which provides minute strokes for alignment of thecenter of a light emitting point.

When both bonding positions match, the vertical mark recognizing means14 is retreated by the recognizing means moving table 15. Next, the headsection 26 is lowered by the vertical drive mechanism 25 so that thelight emitting element 20 and the substrate 22 contact each other. Aposition in a height direction of the head section 26 is detected by ahead height detecting means 24. Contact timing of the light emittingelement 20 and the substrate 22 is detected by the pressing forcedetecting means 32, and the vertical drive motor is switched from aposition control to a torque control. The head height is also monitoredby the head height detecting means 24 during the time when pressing isperformed in the torque control, so that the position in the heightdirection can be controlled.

While a predetermined pressing force is applied between the objects tobe bonded by the torque of a motor, a probe 1 is contacted with anelectrode 1 on an upper surface of the light emitting element, and aprobe 2 is contacted with an electrode 2 on an upper surface of thesubstrate. Preferably, the probe 1 is attached to the head and is movedvertically simultaneously with the head. Alternatively, a portion of thesurface of the holding tool can be plated with metal so that the portioncan serve as a probe. When the probes are contacted with both theelectrodes, the light emitting element is caused to electrically emitlight and function. When a V-shaped groove is provided on a PLCsubstrate and holds an optical fiber, a photometer is set at an end ofthe optical fiber so as to find a position of the light emitting elementwhich provides a maximum light intensity. The positions of the lightemitting element and the substrate are already corrected using thealignment marks with a position accuracy of several micrometers or less.

From that situation, the centers of the light emitting point and theoptical fiber are aligned with an accuracy of the order of submicrons.The center aligning method is performed as follows: the light emittingelement is caused to emit light; light intensity from the optical fiberis measured; and a light amount is measured while changing the positionof the light emitting element to small extent by moving the headvertically, and a maximum point is obtained. The position of the lightemitting element is determined to be at the maximum point, and bondingis performed by low-temperature heating (180° C. or less). Thereby,bonding is achieved in terms of position and electricity. Regarding amethod for recognizing a light emitting point, a position which providesa maximum light amount is generally considered as the light emittingpoint, or alternatively, preferably a light emitting point isrecognized, taking into consideration a contrast state therearound aswell as a maximum value, even though the light emitting point may nothave the maximum value. A position in a height direction of the lightemitting point is determined, depending on a thickness from a lowerportion of the light emitting element to the light emitting point, andtherefore, can be maintained with high accuracy if care is taken duringproduction. However, a horizontal direction depends on a mountingposition accuracy, and therefore, it is difficult to achievehigh-accuracy mounting due to, for example, a position error between thealignment mark and the light emitting point even if the alignment markis used. Therefore, this embodiment is effective.

When an optical fiber is not attached, an outer shape or a referencemark of the PLC substrate is recognized by an object-to-be-bondedrecognizing means. The object-to-be-bonded recognizing means may beeither the vertical mark recognizing means 14 or the light emittingpoint recognizing means, or may be any means. When a substrate mark ispresent on a surface perpendicular to a light emitting direction, anoptical path converting means comprising a prism may be provided on thetip tool or the stage, for example. When a mark is present on theopposite surface, an object-to-be-bonded recognizing means employing IRlight, which transmits through the object to be bonded, is used torecognize an alignment mark 23 formed of a metal, thereby making itpossible to recognize the object to be bonded.

Initially, the position of the V-groove of the PLC substrate isrecognized, and a position which is to be the center of the opticalfiber is recognized. Next, the light emitting point is input to a matriximaging element in the light emitting point recognizing means, which inturn detects the input value. The position of the light emitting elementis adjusted so that a position of the matrix imaging element whichprovides a maximum value matches the center of the optical fiber (targetposition). The light emitting point may be placed at the center positionby shifting the matrix imaging position to the target position. Thelight emitting point recognizing means 33 is shifted using therecognizing means moving table 15 so as to recognize the outer shape orposition of the PLC or the light emitting point, as required. Afterdetermining the position of the light emitting element, bonding isperformed by low-temperature heating (180° C. or less).

Assuming that a mark on an object to be bonded is present in the samedirection as the light emitting direction, if an optical system of thelight emitting point recognizing means is used to recognize the mark onor an outer shape of the object to be bonded, a position at which thenext light emitting point is to be placed is easily known after therecognition of the object to be bonded, so that, preferably, a relativeposition error caused by the recognizing means being providedseparately, a change over time due to thermal expansion, or the like,does not occur. In addition, higher-accuracy measurement can be achievedby holding at least one of the objects to be bonded using a tool havingan optical path converting means comprising a prism or a mirror asillustrated in FIG. 17, and recognizing the object to be bonded and thelight emitting point using the same recognizing means from the side.

For example, when the light emitting point recognizing means and theobject-to-be-bonded recognizing means have different optical systemmagnifications, separate matrix imaging elements are provided. In thiscase, assuming that relative positions of the separate matrix imagingelements are not known, even if the mark of an object to be bonded isrecognized, it cannot be determined where to place the light emittingpoint. Therefore, if the relative positions of the light emitting pointand the mark for recognizing the object to be bonded are recognizedusing a reference jig which previously determines the relativepositions, the relative position relationship can be calibrated.Thereby, it is possible to recognize a light emitting point, and anobject to be recognized on an object to be bonded even when they havedifferent sizes.

After completion of bonding, the suction of the light emitting element20 is released, so that the light emitting element 20 is left on thestage while being mounted on the substrate 22. The substrate 22 isdischarged to the substrate transport conveyer 17 by the substratetransport apparatus 16. The series of operations are ended.

Bonding can be achieved by applying ultrasonic vibration instead ofheating. The method of the present invention can achieve bonding at lowtemperature or at room temperature, so that metal bonding can beachieved in a solid phase without an influence of thermal expansion. Bysuppressing an amplitude to a small level and applying vibration afterpressing, high-accuracy mounting can be achieved without a positionerror.

Next, a variation where a surface light emission type light emittingelement is used will be described, focusing on a difference between thevariation and the above-described example. FIG. 14 is a diagram forexplaining a method of aligning centers of a surface light emittingelement and a substrate having a buried optical fiber and bonding themaccording to the variation. In the case of the surface light emittingelement, the positions of the positioning alignment marks of the lightemitting element 20 and the substrate 22 facing each other arerecognized using the vertical mark recognizing means 14, the positionsof the light emitting element 20 and the substrate 22 are aligned, andthe probes are contacted with both the electrodes on the substrate whilea predetermined pressing force is applied between electrodes which areto be bonding surfaces, so that the light emitting element is caused toelectrically emit light and function. The light emitting pointrecognizing means 33 is shifted to an end of the optical fiber buried inthe substrate 22 using the recognizing means moving table 15, to measurelight intensity. The positions of the light emitting element and thesubstrate are already corrected using the alignment marks with aposition accuracy of several micrometers or less. From that situation,the centers of the light emitting point and the optical fiber arealigned with an accuracy of the order of submicrons.

The center aligning method is performed as follows: the light emittingelement is caused to emit light; light intensity from the optical fiberis measured; and a light amount is measured while changing the positionof the light emitting element to small extent by moving the headvertically, and a maximum point is obtained. The position of the lightemitting element is determined to be at the maximum point, and bondingis performed by low-temperature heating (180° C. or less). Thereby,bonding is achieved in terms of position and electricity. Regarding amethod of recognizing a light emitting point, a position which providesa maximum light amount is generally considered as the light emittingpoint, or alternatively, preferably a light emitting point isrecognized, taking into consideration a contrast state therearound aswell as a maximum value, even though the light emitting point may nothave the maximum value. A position in a height direction of the lightemitting point is determined, depending on a thickness from a lowerportion of the light emitting element to the light emitting point, andtherefore, can be maintained with high accuracy if care is taken duringproduction. However, a horizontal direction depends on a mountingposition accuracy, and therefore, it is difficult to achievehigh-accuracy mounting due to, for example, a position error between thealignment mark and the light emitting point even if the alignment markis used. Therefore, this embodiment is effective.

When an optical fiber is not buried in the substrate, and the substrateis a submount substrate having an optical path hole, an outer shape or areference mark of the submount substrate is recognized by anobject-to-be-bonded recognizing means. The object-to-be-bondedrecognizing means may be either the vertical mark recognizing means 14or the light emitting point recognizing means, or may be any means. Whena substrate mark is present on a perpendicular surface, an optical pathconverting means comprising a prism may be provided on the tip tool orthe stage, for example. When a mark is present on the opposite surface,an object-to-be-bonded recognizing means employing IR (infrared) light,which transmits through the object to be bonded, is used to recognize analignment mark 23 formed of a metal, thereby making it possible torecognize the object to be bonded.

If a position where the light emitting point is to be placed ispreviously recognized by recognizing a position of the optical path holeof the submount or a position of the submount based on the outer shapeor the mark, center alignment can be achieved by directly inputting thelight emitting point to a matrix imaging element, detecting the inputvalue, and adjusting the position of the light emitting element so thata position of the matrix imaging element which provides a maximum valueof the input value matches a target matrix imaging element position. Thelight emitting point may be placed at the center position by shiftingthe matrix imaging position to the target position. Regarding a methodof recognizing a light emitting point using a matrix imaging means, animaging element position which provides a maximum value is generallyconsidered as the light emitting point, or alternatively, preferably alight emitting point is recognized in units of a subpixel of the imagingelement, taking into consideration a contrast state therearound as wellas a maximum value, even though the light emitting point may not havethe maximum value. Assuming that a mark on an object to be bonded ispresent in the same direction as the light emitting direction, if anoptical system of the light emitting point recognizing means is used torecognize a mark on or an outer shape of an object to be bonded, aposition at which the next light emitting point to be placed is easilyknown after the recognition of the object to be bonded, so that,preferably, a relative position error caused by the recognizing meansbeing provided separately, a change over time due to thermal expansion,or the like, does not occur.

In addition, higher-accuracy measurement can be achieved by holding atleast one of the objects to be bonded using, for example, a tool havingan optical path converting means comprising a prism or a mirror asillustrated in FIG. 18, and recognizing the object to be bonded and thelight emitting point using the same recognizing means from the side. Thelight emitting point recognizing means 33 is shifted using therecognizing means moving table 15 so as to recognize the outer shape orposition of the substrate or the light emitting point, as required.After completion of bonding, the suction of the chip 20 is released, sothat the chip 20 is left on the stage while being mounted on thesubstrate 22. The substrate 22 is discharged to the substrate transportconveyer 17 by the substrate transport apparatus 16. The series ofoperations are ended.

By providing an ultrasonic transmitter or a horn instead of the lightemitting element holding tool 8 and/or the tip tool 9, ultrasonicvibration is applied instead of heating during the bonding, therebymaking it possible to more easily achieve metal bonding in a solidphase. In this case, the method of the present invention can achievebonding at low temperature or room temperature, so that metal bondingcan be achieved in a solid phase without an influence of thermalexpansion. By suppressing an amplitude to a small level and applyingvibration after pressing, high-accuracy mounting can be achieved withouta position error.

Although a light emitting element and a substrate have been described inthe example of the fifth embodiment, the present invention encompassesan object to be bonded which is a functional device which requiresposition adjustment in addition to light emitting elements.

Sixth Embodiment

Next, a sixth embodiment of the present invention will be described indetail. This embodiment is significantly different from theabove-described first to fifth embodiments in that, before bondingobjects to be bonded, the bonding portions are subjected to theabove-described leveling (see FIGS. 8 to 11). Hereinafter, specificfeatures of this embodiment will be described.

In order to perform room-temperature bonding while keeping a solid phasein the atmospheric air, the bonding surfaces (portions to be bonded) ofobjects to be bonded are previously etched by several nanometers in avacuum using Ar plasma (an energy wave) to remove adhering substances.When bonding is performed in the atmospheric air after cleaning, anadhering substance layer is formed on the bonding surface, so thatbonding is not achieved only by contacting. However, since the adheringsubstance layer is thin immediately after cleaning, a new surfaceappears due to pressing, which allows bonding. As illustrated in FIG. 7,room-temperature bonding can be achieved by pressing even in theatmospheric air if the object to be bonded is not allowed to stand afterdry cleaning. This may be because, although a thin adhering substancelayer is formed on the bonding surface, the layer is so thin that it canbe crushed by pressing.

In this embodiment, when the bonding portion is subjected to leveling, asufficient bonding strength can be obtained using a pressing force of150 MPa, while a pressing force of 300 MPa is required when leveling isnot performed. This may be because a pressing force which is required tocrush a rough portion of the bonding portion so as to contact bondingportions together varies, due to variations in height of the bumps 20 aand 22 a or the surface roughness. In the case of an ordinary bump whichwas not subjected to leveling, the height variation was 2 μm and thesurface roughness was 200 nm. However, after performing leveling, boththe height variation and the surface roughness of a bump were 50 nm orless. Therefore, it is considered that the bonding load was able to bereduced. The leveling indicates that the height or surface roughness ofbumps is corrected to be uniform by pressing the bump against areference support 40 having a high flatness as illustrated in FIG. 10.Leveled chips may be previously arranged, or may be leveled using abonding apparatus before bonding to a substrate.

In order to crush the bonding portion to achieve bonding, the bondingmetal needs to have a low hardness. In this embodiment as in theabove-described embodiments, a metal bonding portion which has ahardness of 200 Hv or less was used, and particularly when gold orcopper was used, firm bonding was able to be achieved. Note that, whenleveling was used, bonding was able to be achieved by a pressing forceof 150 MPa or less. Particularly, when a bonding portion was formed ofgold, a low hardness was obtained and oxidation did not occur even inthe atmospheric air. Thus, gold is an effective metal.

Flipchip bonding for a semiconductor chip which has a number ofelectrode portions (metal bumps) is expected to provide mounting havinga high accuracy ranging from minute pitch electrodes to severalmicrometers or less, and is desired to be performed at a low temperatureof 180° C. or less, preferably room temperature, because of an influenceof heat to a semiconductor. Therefore, this embodiment is particularlyeffective to the flipchip bonding.

The semiconductor chip may be in any form, such as a chip, a wafer, orthe like. The metal bump may be a plurality of shapes separatelyprovided or a shape in which a certain continuous region is confined.The entire surface may be a bonding surface.

Although a chip and a substrate have been described in the example ofthe sixth embodiment, an object to be bonded may be formed of materialsother than semiconductors.

Seventh Embodiment

Hereinafter, a seventh embodiment of the present invention will bedescribed in detail. FIG. 19 illustrates the seventh embodiment of thebonding apparatus of the present invention. In the seventh embodiment,an apparatus for bonding a chip 20 formed of a semiconductor (a firstobject to be bonded) and a substrate 22 formed of a wafer (a secondobject to be bonded) will be described as an example. A bonding surfaceof the chip 20 has a plurality of bumps (metal electrodes) 20 a whichare electrodes and are formed of gold, and a bonding surface of thesubstrate 22 has a metal pad 22 a which is an electrode and is providedat a position which allows to face the metal electrode of the chip. Themetal electrode of the chip and the metal electrode of the substrate arebonded together by pressing after a treatment using an energy wave.

The bonding apparatus roughly includes a bonding mechanism 27 includinga vertical drive mechanism 25 and a head section 26, a mountingmechanism 28 including a stage 10 and a stage table 12, a positionrecognizing section 29, a transport section 30, and a control apparatus31. The vertical drive mechanism 25 moves the head section 26 verticallyusing a vertical drive motor 1 and a bolt-nut mechanism 2 while beingguided by a vertical guide 3. The head section 26 is guided verticallyby a head escape guide 5, and contacts a pressing force detecting means32 for detecting a pressing force and the vertical drive mechanism whilebeing pulled by a head own-weight counter 4 for canceling the head's ownweight and pressing the head against the pressing force detecting means32. The head section 26 is composed of a chip holding tool 8 which sucksand holds the chip 20, a tip tool 9, a head's alignment table 7 whichhas movement axes of translation and rotation and performs positioncorrection, and a head holding section 6 which supports them. A heatingheater is buried and provided inside the chip holding tool. The mountingmechanism 28 is composed of the stage 10 which sucks and holds thesubstrate 22, and the stage table 12 which has movement axes oftranslation and rotation and performs alignment of positions of a chipand a substrate. A stage heater 11 is included in the stage 10. Thebonding mechanism is coupled with a frame 34 and is linked to a pedestal35 via four supporting poles 13 provided around a pressing center. Theposition recognizing section 29 is composed of a vertical markrecognizing means 14 which is inserted between a chip and a substratefacing each other and recognizes alignment marks for recognizingpositions of the chip (upper position) and the substrate (lowerposition), and a recognizing means moving table 15 which moves thevertical mark recognizing means 14 horizontally and/or vertically.

The transport section 30 includes a substrate transport apparatus 16 anda wafer cassette 243 which transport the substrate 22, and a chip supplyapparatus 18 and a chip tray 19 which transport the chip 20. In order tocontinuously perform cleaning and bonding, a cleaning machine 241 islinked with the bonding apparatus and the transport means. The chip trayand the wafer are transported into the cleaning machine, followed bycleaning and removal, as required. The chip tray 19 is supplied from orstored into a chip tray cassette 242. The wafer 22 is supplied from orstored into the wafer cassette 243. A control section 31 includes acontrol of the whole apparatus and an operation section. Particularly ina pressing force control, the control section 31 controls the torque ofthe vertical drive motor 1 based on a signal from the pressing forcedetecting means 32 to control a pressing force for bonding.

Next, a series of operations will be described. The cleaned chip 20 issupplied from the chip tray 19 to the chip holding tool 8 by the chipsupply apparatus 18, and is sucked and held by the chip holding tool 8.The cleaned substrate (wafer) 22 is supplied to the stage 10 by thesubstrate transport apparatus 16, and is sucked and held by the stage10. The vertical mark recognizing means 14 is inserted between the chip20 and the substrate 22 whose bonding surfaces face each other by therecognizing means moving table 15. Positions of the positioningalignment marks of the chip 20 and the substrate 22 facing each otherare recognized by the vertical mark recognizing means 14. Using the chip20 as a reference, the position of the substrate 22 is moved in atranslation direction and a rotation direction by the stage table 12 forthe purpose of alignment. During alignment, position correction may beperformed by the stage table 12 and the head's alignment table, or onlyby the head's alignment table. Only either of the tables may beprovided.

When both the bonding positions match each other, the vertical markrecognizing means 14 is retreated by the recognizing means moving table15. Next, the head section 26 is lowered by the vertical drive mechanism25 so that the chip 20 and the substrate 22 contact each other. Aposition in a height direction of the head section 26 is detected by ahead height detecting means 24. Contact timing of the chip 20 and thesubstrate 22 is detected by the pressing force detecting means 32, andthe vertical drive motor is switched from a position control to a torquecontrol. The head height is also monitored by the head height detectingmeans 24 during the time when pressing is performed in the torquecontrol, so that the position in the height direction can be controlled.After completion of bonding, the suction of the chip 20 is released, sothat the chip 20 is left on the stage while being mounted on thesubstrate 22. By continuously bonding chips to a substrate (wafer),mounting is completed. The substrate 22 is discharged to the wafercassette 243 by the substrate transport apparatus 16. The series ofoperations are ended.

Note that, assuming that a plurality of chips are bonded onto a singlewafer, if the number of chips is large, it takes a long time. In orderto achieve room-temperature bonding in the atmospheric air, bonding isperformed within about one hour after dry cleaning. This is because, ifotherwise, adhering substances increase on a bonding surface, so thatbonding cannot be performed. Therefore, dry cleaning (surface activatingtreatment) is preferably performed again with a low-pressure plasma(energy wave) within one hour, preferably 30 minutes. Therefore, thecleaning machine 241 is coupled with the bonding apparatus so that, whena chip is bonded onto a wafer, after a predetermined time has passed,the wafer is temporarily transported from the stage to the cleaningmachine, in which cleaning is in turn performed again. After cleaning,the wafer is set on the stage again to start chip bonding. Thereby, anumber of chips can be continuously bonded to a wafer in the atmosphericair at low temperature.

Eighth Embodiment

Hereinafter, an eighth embodiment of the present invention will bedescribed in detail. Firstly, an object to be bonded of this embodimentwill be described in detail with reference to FIG. 24. As illustrated inFIG. 24, in this embodiment, a device 829 and a lid 830 are bondedtogether. A contour-shaped gold plating 831 having a thickness of 1 μmor more is formed as a bonding portion on a bonding surface of thedevice 829. A thin gold film 832 is formed on a bonding surface of thelid 830 by sputtering or flash plating. Note that the thick film plating831 and the thin film 832 may be reversely formed on the lid 830 and thedevice 829, respectively. FIG. 24 illustrates a chip form.Alternatively, as illustrated in FIG. 25, bonding is most effectivelyperformed on a wafer before dicing.

FIG. 20 illustrates a wafer bonding apparatus according to the eighthembodiment of the present invention. In this embodiment, a wafer whichis an object to be bonded serving as a lid, is held at an upper portionand a wafer which serves as a device is held at a lower portion whilethe wafers face each other. In this situation, a chamber is closed, boththe objects to be bonded are etched in a vacuum using Ar plasma beforebeing contacted each other and bonded together by pressing. In thisapparatus, in some cases, heating is performed at a low temperature of180° C. or less so as to increase strength. The apparatus is configuredto have a head section which holds an upper wafer 807 (the lid 830) andperforms a vertical movement control and a pressing control using a Zaxis 801, and a stage section which holds a lower wafer 808 (the device829) and may align the wafers.

The Z axis 801 includes a pressure detecting means, and performs apressing force control by performing feedback with respect to a torquecontrol of a Z-axis servo motor. A chamber wall 803 which can be liftedand lowered by an actuator additionally provided is lowered, and iscontacted via a fixing packing 805 to a chamber support 810. In thissituation, the chamber is evacuated, reaction gas is introduced, aplasma treatment is performed, evacuation is performed, replacement withfilling gas is performed when the chamber is filled with filling gas,and the head section is lowered to contact and press both waferstogether so that the wafers are bonded. The chamber wall 803 is sealedusing an O ring in a manner which allows the chamber wall to be liftedand lowered, or alternatively may be received at a place where a shaftis narrowed or at an outer circumference of a piston. In some cases, anupper electrode 806 and a lower electrode 809 may be provided with aheating heater which can perform heating during bonding.

As illustrated in FIGS. 21 A to 21C; an operation will be described insequence. As illustrated in FIG. 21A, while the chamber wall 803 is inthe lifted state, the upper wafer 807 is held by the upper electrode(energy wave emitting means) 806. The holding method may be a mechanicalchucking method, or desirably an electrostatic chuck method. Thereafter,the lower wafer 808 is held by the lower electrode (energy wave emittingmeans) 809. Next, as illustrated in FIG. 21B, the chamber wall 803 islowered to be contacted via the fixing packing 805 to the chambersupport 810. The chamber wall 803 is sealed from the atmosphere by asliding packing 804. Therefore, by opening a discharge valve 814 whilean intake valve 813 is closed, the chamber is evacuated using a vacuumpump 815, thereby making it possible to increase the degree of vacuum inthe chamber.

Next, as illustrated in FIG. 21C, the chamber is filled with reactiongas including Ar. By controlling a discharge amount at the dischargevalve 814 and a gas intake amount at the intake valve 813 while thevacuum pump 815 is being operated, the chamber can be filled with thereaction gas while keeping a certain degree of vacuum. As illustrated inFIGS. 21D and 21E, in this embodiment, the chamber is initially filledwith Ar gas, and a plasma generating voltage is applied to the lowerelectrode 809 by an alternating power supply where the degree of vacuumis about 10⁻² Torr, thereby generating plasma to etch and clean asurface of the lower wafer 808 using the Ar plasma. Next, by applying avoltage from a similar alternating power supply to the upper electrode806, the upper wafer is etched and cleaned using Ar plasma. Next, asillustrated in FIG. 21B, the chamber is evacuated to discharge Ar. Insome cases, by performing evacuation while heating both the electrodesat about 100° C., Ar which adheres to a surface or is implanted into apart is discharged. Thereafter, replacement with filling gas isperformed when the chamber is filled with filling gas.

Next, as illustrated in FIG. 21F, a piston type head 802 is lowered bythe Z axis 801 in a vacuum or in filling gas while the chamber wall 803contacts the Z axis 801 via the sliding packing 804, so that both thewafers are contacted with each other in a vacuum or in filling gas, andboth the wafers are bonded together by pressing. The inside of thechamber is blocked from an external atmosphere by the sliding packing804 between the chamber wall 803 and the Z axis 801, whereby the pistontype head section can be lowered while being held in a vacuum or infilling gas. In some cases, the wafers are simultaneously heated toabout 180° C. by the heaters included in both the electrodes, therebyincreasing strength. Thereafter, as illustrated in FIG. 21G, anatmospheric air is supplied into the chamber so that the pressure of thechamber is put back to the atmospheric pressure, the head section islifted, and the bonded wafers are removed out. A method of changing twogases (Ar and the atmospheric air or nitrogen) in a single chamber, canselect and supply Ar and the atmospheric gas using a gas switch valve816. After Ar is initially selected to fill the chamber, the intakevalve 813 is closed to evacuate the chamber to discharge Ar. Thereafter,the gas switch valve 816 is switched to the atmospheric gas, and theintake valve 813 is opened to fill the chamber with the atmospheric air.When the chamber is opened, the atmospheric air can be released.

In some cases, regarding bonding of objects to be bonded, a device and alid may be bonded together after the positions of the device and the lidare aligned. FIG. 22 illustrates a method of performing alignment beforeevacuation. Upper alignment marks 823 are attached to two portions ofthe upper wafer 807, and lower alignment marks 824 are attached to twosimilar portions of the lower wafer 808. A two-side recognizing means825 is inserted between both the wafers, and the upper and lower markpositions are read using the recognizing means. The two-side recognizingmeans 825 splits upper and lower mark images using a prism 826, so thatthe upper and lower mark images are separately read by an upper markrecognizing means 827 and a lower mark recognizing means 828. Thetwo-side recognizing means 825 is moved using a table having the X and Yaxes and, in some cases, the Z axis, thereby making it possible to reada mark at any arbitrary position. Thereafter, the position of the lowerwafer 808 is corrected and shifted to the position of the upper wafer807 using an alignment table 820. After shifting, the two-siderecognizing means 825 can be inserted again to repeat correction,thereby improving accuracy.

FIG. 23 illustrates a method capable of performing alignment even afterevacuation and before bonding. Upper alignment marks 823 are attached totwo portions of the upper wafer 807, and lower alignment marks 824 areattached to two portions of the lower wafer 808. The upper and lowermarks have shapes which can be recognized in the same visual field evenif they overlap each other. After a plasma treatment, both wafers areplaced close to each other, and the upper and lower alignment marksformed of a metal are simultaneously recognized and the positionsthereof are read by an IR recognizing means 822, where a mark readtransparent portion 819, a glass window 821, and the lower wafer aretransparent with respect to the upper and lower alignment marks. When acorrect depth of focus is not obtained, reading is performed by movingthe IR recognizing means 822 vertically. The IR recognizing means 822 ismoved using a table having the X and Y axes and, in some cases, the Zaxis, thereby making it possible to read a mark at any arbitraryposition. Thereafter, the position of the lower wafer 808 is correctedand shifted to the position of the upper wafer 807 using an alignmenttable 820. After shifting, the IR recognizing means 822 can be usedagain to repeat correction, thereby improving accuracy.

Note that, when a bonding portion is formed of gold, the bonding portionis not corroded by filling gas even if the filling gas is not inert gas,so that the filling gas does not have an influence on bonding.Therefore, other gases as well as inert gas can be applied in thisembodiment.

Etching is preferably performed using Ar plasma in terms of efficiency,however, etching may be performed using other gases, such as nitrogen,oxygen, and the like.

Regarding a method of subjecting an object to be bonded to a plasmatreatment (a treatment using an energy wave, a surface activatingtreatment), a wafer held on an electrode surface to which an alternatingpower supply is connected is preferably cleaned in terms of efficiency,however, the electrode may be placed at a position other than the waferholding position and the wafer may be cleaned (a surface activatingtreatment) in terms of uniformity or a reduction in damage.

In the configuration in which the IR recognizing means reads a mark, apassage of an IR light source in space or the like between the mark readtransparent portion 819, the glass window 821, and the alignment tableis not limited to space and glass, and may be formed of a material whichtransmits IR light. Instead of reflected light, transmitting light maybe used, where a light source is provided on the opposite side of the IRrecognizing means.

An elastic material may be provided on a surface of at least one of theobjects-to-be-bonded holding means (the head or the stage), and whenobjects to be bonded are bonded together, pressing may be performed viathe elastic material with respect to both the objects to be bonded. Withsuch a configuration, it is possible to increase the parallelism of theobjects to be bonded. Also, it is possible to increase the flatness ifan object to be bonded is thin.

The object-to-be-bonded holding means may be held on the stage and/orthe head via a spherical bearing, and objects to be bonded may becontacted and pressed by each other during or before bonding so that thetilt of at least one of the objects to be bonded can match the tilt ofthe other. With such a configuration, bonding can be performed,increasing the parallelism (see FIG. 29).

The bonding apparatus of this embodiment is configured to be able toperform a batch process from a surface activating treatment (cleaning)of objects to be bonded to bonding of the objects to be bonded, however,a surface activating apparatus for performing a surface activatingtreatment using an energy wave and a bonding apparatus for performingbonding may be separated.

Ninth Embodiment

A ninth embodiment of the present invention will be described in detailwith reference to FIG. 29. This embodiment provides an apparatus forclosing a chamber while holding wafers (objects to be bonded) facingeach other vertically, treating the wafers with Ar plasma and oxygenplasma, and bonding the wafer together, and in some cases, heating thewafers to increase strength. The apparatus includes a head section whichholds an upper wafer 537 and performs a vertical movement control and apressing control using a Z axis 531, and a stage section which holds alower wafer 538 and, in some cases, aligning wafers. The Z axis 531includes a pressure detecting means, and performs a pressing forcecontrol by performing feedback with respect to a torque control of a Zaxis servo motor. A chamber wall 533 which can be lifted and lowered byan actuator additionally provided is lowered, and is contacted via afixing packing 535 to a chamber support 540. In this situation,evacuation is performed, reaction gas is introduced, a plasma treatment(surface activating treatment) is performed, and the head section islowered to bond both wafers together.

In some cases, the upper electrode 536 and the lower electrode 539 maybe provided with a heating heater which can perform heating duringbonding. Thereafter, the atmospheric air is supplied into the chamber sothat the pressure of the chamber is put back to the atmosphericpressure, the head section is lifted, and the bonded wafers are removedout. In some cases, bonding can be performed after alignment of thepositions of both the wafers. When alignment is performed in theatmospheric air, an optical system having two visual fields (upper andlower) is inserted between both objects to be bonded, and the head orthe stage is moved and corrected in horizontal and rotationaldirections. When alignment is performed in a vacuum, a portion of thestage may be formed of a transparent material so as to be transparentwith respect to both the objects to be bonded, where light transmits thetransparent material from the bottom, and alignment marks formed of ametal may be read, and the head or the stage may be moved and correctedin horizontal and rotational directions.

A lower electrode (object-to-be-bonded holding means) 539 is held by acopying mechanism (spherical bearing) 550, so that the wafers arecontacted and pressed by each other during or before bonding of thewafers to cause the tilt of the lower wafer 538 to match the tilt of theupper wafer 537 on the upper electrode 536. With such a configuration,the wafers (objects to be bonded) can be bonded together whileincreasing the parallelism of the wafers (see FIG. 29). The copyingmechanism 550 may have a lock mechanism which selects lock/free, and isnormally in a locked state, and when copying, is in a free state. Thecopying mechanism 550 can be locked after the parallelism is onceincreased, and while holding this state, the wafers can also besubjected to a plasma treatment (energy wave treatment) and alignment,followed by bonding. Therefore, since alignment is performed afterincreasing the parallelism, the wafers can be bonded together without aposition error.

Tenth Embodiment

A tenth embodiment of the present invention will be described in detailwith reference to FIG. 30. This embodiment provides a bonding apparatusin which objects to be bonded are bonded together in the atmospheric airafter being subjected to plasma cleaning (surface activating treatment)in a vacuum. At least one of the objects to be bonded is transportedinto a cleaning chamber, which is linked to a transport means fortransporting the objects to be bonded to a bonding section aftercleaning, and the next objects to be bonded are cleaned during bonding.

Objects to be bonded whose bonding surfaces are formed of gold or coppercan be previously separately surface-activated by a plasma treatment ina vacuum chamber, and can be removed into the atmospheric air, followedby bonding. The cleaned objects to be bonded are transported to abonding section by a transport means, and the next objects to be bondedare cleaned during bonding. Therefore, cleaning can be performedparallel to bonding, thereby making it possible to save time.

When balance is not attained on a one-by-one basis, a plurality ofobjects to be bonded may be placed on a tray or the like and may besimultaneously cleaned. When a continuous object to be bonded isprovided on a reel, the object to be bonded may be seized via a packingby a chamber door to be subjected to a plasma treatment. When alignmentis performed before bonding, a recognizing means 663 having two (upperand lower) visual fields may be inserted between both objects to bebonded, and the head or the stage may be moved and corrected inhorizontal and rotational directions. The recognizing means 663 havingtwo (upper and lower) visual fields can be shifted to any arbitraryposition by a recognizing means moving table to perform positionmeasurement.

Note that a means for holding an object to be bonded in a vacuum isdesirably of an electrostatic chuck type, or may be of a mechanicalchuck type. Preferably, objects to be bonded sucked and held by vacuumare tightly attached together in the atmospheric air before mechanicalchucking, resulting in an improvement in tight attachment.

Eleventh Embodiment

Next, an eleventh embodiment of the present invention will be describedin detail with reference to FIG. 31. In this embodiment, an apparatusfor bonding an upper wafer (first object to be bonded) and a lower wafer(second object to be bonded) will be described as an example. Firstly, aconfiguration of the apparatus will be described. A head 907 which holdsthe upper wafer and a stage 908 which holds the lower wafer are providedin a vacuum chamber 911. The head includes a Z-axis lifting/loweringmechanism (vertical drive mechanism) 902 to which a torque controllifting/lowering drive motor 901 is linked, a θ-axis mechanism whichrotates the Z-axis lifting/lowering mechanism 902, and an XY alignmenttable 906 which moves and aligns the head section in X and Y horizontaldirections, which provide an aligning/moving means for the X, Y, and θdirections and a lifting/lowering means for the Z direction.

A pressing force detected by a pressure detecting means 904 duringbonding is fed back to the torque control lifting/lowering drive motor901, thereby switching between a position control and a pressing forcecontrol. Also, the pressure detecting means 904 can be used to detectcontact of objects to be bonded. The XY alignment table 906 can use ameans which can be used in a vacuum. Since the Z- and θ-axis mechanismsare placed outside a vacuum chamber, the head section is blocked fromthe outside via a bellows 905 in a manner which allows the head sectionto move.

The stage 908 can be slid between a bonding position and a standbyposition by a slide moving means 929. A linear scale for high-accuracyguidance and position recognition is attached to the slide moving means,so that a stop position between the bonding position and the standbyposition can be maintained with high accuracy. The moving means is builtin the vacuum chamber. However, if the moving means can be providedoutside and linked via a linking rod with packing, a cylinder, a linearservo motor, and the like can be provided outside. Alternatively, a ballscrew can be provided in a vacuum, and a servo motor can be providedoutside. Any moving means may be used.

Although the object-to-be-bonded holding means of the head and the stagemay be of a mechanical chucking type, an electrostatic chuck ispreferably provided. The object-to-be-bonded holding means also includesa heating heater, and also serves as a plasma electrode (energy waveemitting means), i.e., has three functions: holding means; heatingmeans; and plasma generating means. Regarding a decompressing means, avacuum pump 917 is coupled with a gas discharge pipe 915, and a gasdischarge valve 916 is opened or closed so as to control a flow rate, sothat the degree of vacuum is controlled. Regarding an intake portion, anintake gas switching valve 920 is linked to an intake pipe 918, and agas intake valve 919 is opened or closed so as to control a flow rate.

Regarding intake gas, two plasma reaction gases can be linked. Forexample, Ar and oxygen can be linked. As the other one, the atmosphericair for releasing the atmospheric air or nitrogen is linked. The degreeof vacuum and the reaction gas concentration can be controlled to beoptimum values by a control of a flow rate, including opening or closingof the gas intake valve 919 and the gas discharge valve 916. Inaddition, a vacuum pressure sensor can be provided in the vacuum chamberto perform automatic feedback.

Alignment mark recognizing means comprising an optical system foralignment are provided outside the vacuum chamber above the stagestandby position and below the head. Regarding the number of recognizingmeans, at least one needs to be provided for the stage and at least oneneeds to be provided for the head. Assuming that a small object, such asa chip, is recognized, if an alignment mark has a shape whoseθ-direction component can be read or two marks are provided in onevisual field, a single recognizing means is sufficient to read. However,when an object having a large radius, such as a wafer, is used as inthis embodiment, two recognizing means are preferably provided at eachend, thereby making it possible to read with high θ-direction accuracy.

The recognizing means may also be provided with a means which can movein a horizontal direction or a focusing direction, thereby reading analignment mark placed at any arbitrary position. The recognizing meansmay include a camera having an optical lens for visible light or IR(infrared) light, for example. The vacuum chamber is provided with awindow formed of a material which is transparent with respect to anoptical system of the recognizing means, such as glass. An alignmentmark on an object to be bonded in the vacuum chamber is recognized viathe window. Alignment marks are provided on objects to be bonded (e.g.,surfaces facing each other of an upper wafer or a lower wafer), therebymaking it possible to recognize a position with high accuracy. Althoughthe alignment mark is preferably in any specific shape, a portion of acircuit pattern provided on a wafer may be used as an alignment mark.When a mark is not present, an outer shape, such as an orientation flator the like, can be used.

The alignment marks of both the upper and lower wafers are read at thestage standby position, the stage is shifted to a bonding position, andthe head is moved so as to perform alignment in the X, Y, and θdirections. In order to reflect the result of reading at the standbyposition at the bonding position, accuracy is required so that arelative movement distance vector between the stage standby position andthe bonding position repeatedly has the same result. Therefore, a guidewhich has high repetition accuracy is used, and a linear scale whichreads position recognition at both the sides with high accuracy, areprovided.

When stop position accuracy is improved by feeding a linear scale backto the moving means, and the moving means is one which is like a simplecylinder or one which has a backlash, such as a bolt-nut mechanism, thelinear scale is read at both the stop positions, an excess or a shortageis corrected when the head's aligning/moving means is moved, therebymaking it possible to easily achieve high accuracy. When fine alignmentis performed with nano-level accuracy, rough positioning is performed,and thereafter, while the upper wafer and the lower wafer are close toeach other at a distance of about several micrometers, a visiblelight/IR recognizing means is used as the head's recognizing means, anda transparent hole or a transparent material is provided at an alignmentmark position of the stage, so that alignment marks on both the wafersare simultaneously recognized via the transparent stage from the bottom,and alignment can be achieved again in the X, Y, and θ directions. Whenthe recognizing means has a moving means in a focusing direction, theupper and lower wafers can be separately recognized. However, it ispreferable in terms of accuracy that the wafers be placed close to eachother and be simultaneously recognized.

Regarding the fine alignment, accuracy can be improved by repetition ofalignment. The θ direction is affected by center displacement.Therefore, after the θ reaches within a predetermined range, alignmentis performed only in the X and Y directions, thereby making it possibleto improve the accuracy to a nano-level. Regarding the image recognizingmeans, recognition accuracy higher than the resolution of infrared canbe obtained by using a subpixel algorithm. When alignment is performedafter the wafers are placed close to each other, a Z movement amountrequired during bonding is within a minimum limit of several micrometersor less, so that play or tilt with respect to the Z movement can beminimized, resulting in high accuracy, i.e., nano-level bondingaccuracy.

Next, an operation flow will be described with reference to FIGS. 32A to32K. Firstly, as illustrated in FIG. 32A, while a front door of thevacuum chamber is open, the upper wafer and the lower wafer are held onthe stage and the head. The wafers may be manually set or may beautomatically loaded from a cassette. Next, as illustrated in FIG. 32B,the front door is closed, and the vacuum chamber is decompressed. Inorder to remove impurities, the pressure is preferably reduced to 10⁻³Torr or less. Next, as illustrated in FIGS. 32C and 32D, plasma reactiongas (e.g., Ar) is supplied, and a plasma generating voltage is appliedto plasma electrodes, where the degree of vacuum is constant at, forexample, about 10⁻² Torr, so that plasma is generated.

Generated plasma ions go toward and strike a surface of a wafer held byan electrode which is connected to a power supply, so that adheringsubstances, such as an oxide film, an organic substance layer, or thelike, on the surface is etched, resulting in surface activation. At thesame time, both the wafers can be cleaned. Alternatively, the wafers canbe alternately cleaned by switching one matching box. The pressure ispreferably reduced to 10⁻³ Torr or less so as to remove reaction gas oretched matter after or during cleaning. In order to remove Ar implantedin the bonding surface, the wafers can be heated to about 100 to 200° C.as well.

Next, as illustrated in FIG. 32E, alignment marks on the upper and lowerwafers are read at the stage standby position using the head's andstage's recognizing means in a vacuum, and the positions are recognized.Next, as illustrated in FIG. 32F, the stage is slid and shifted to abonding position. In this case, a relative movement between therecognized standby position and the bonding position to which the stageis slid and shifted, is performed with high accuracy using a linearscale. When nano-level accuracy is required, a step indicated with FIG.32G is added. After rough positioning, while the upper wafer and thelower wafer are close to each other at a distance of about severalmicrometers, a visible light/IR recognizing means is used as the head'srecognizing means, and a transparent hole or a transparent material isprovided at an alignment mark position of the stage, so that alignmentmarks on both the wafers are simultaneously recognized by infraredtransmission via the transparent stage from the bottom, and alignmentcan be achieved again in the X, Y, and θ directions. In this case,accuracy can be improved by repetition of alignment. The θ direction isaffected by center displacement. Therefore, after the θ reaches within apredetermined range, alignment is performed only in the X and Ydirections, thereby making it possible to improve the accuracy to anano-level.

Next, as illustrated in FIG. 32H, the head is lowered to contact boththe wafers together, and the position control is switched to thepressing force control, in which pressing is in turn performed. Thecontact is detected by the pressure detecting means and a heightposition is recognized. In this situation, a value obtained by thepressure detecting means is fed back to the torque controllifting/lowering drive motor to perform a pressing force control so asto achieve a set pressure. Also, heat is applied during bonding asrequired. After contacting at room temperature, heating can be performed(temperature is increased) while keeping the accuracy. Next, asillustrated in FIG. 32I, the head's holding means is released, and thehead is lifted. Next, as illustrated in FIG. 32J, the stage is movedback to the standby position, and the vacuum chamber is released toatmospheric air. Next, as illustrated in FIG. 32K, the front door isopened, the bonded upper and lower wafers are removed. The wafers areunloaded onto a cassette manually or preferably automatically.

A metal electrode can be provided on an opposing surface of at least oneof the objects to be bonded during cleaning (energy wave treatment), anda metal film can be formed of a metal forming an electrode provided on abonding surface of the object to be bonded by sputtering, andthereafter, the objects to be bonded can be bonded together. The objectsto be bonded are moved so that plasma can be generated while the bondingsurfaces of the objects to be bonded do not face each other. Therefore,a metal for sputtering is provided on a surface facing the bondingsurface (bonding portion), and the metal is used as an electrode forgenerating plasma, so that the metal is sputtered on a surface (bondingsurface) of the object to be bonded, thereby forming a thin metal filmformed of the metal. Different metals for sputtering can be used betweenthe head and the stage.

Different plasma reaction gases can be used between one and the otherobjects to be bonded, which can be in turn cleaned separately.

An elastic material may be provided on a surface of at least one of theobjects-to-be-bonded holding means, and when objects to be bonded arebonded together, pressing may be performed via the elastic material withrespect to both the objects to be bonded. With such a configuration, itis possible to increase the parallelism of the objects to be bonded.Also, it is possible to increase the flatness if an object to be bondedis thin.

The object-to-be-bonded holding means may be held on the stage and/orthe head via a spherical bearing. With such a configuration, objects tobe bonded may be contacted and pressed by each other during or beforebonding so that the tilt of at least one of the objects to be bonded canmatch the tilt of the other. Therefore, bonding can be performed afterincreasing the parallelism.

Since the bonding surfaces of objects to be bonded are surface-activatedwith a plasma treatment before bonding, the heating temperature duringbonding of the objects to be bonded can be set at 180° C. or less whichis below 183° C. which is the melting point of conventional tin-leadsolder (solid phase bonding). Also, bonding is preferably possible at100° C. or less, even at room temperature.

By attaching semiconductors using the above-described method, athree-dimensional structure can be preferably obtained, resulting asemiconductor apparatus having a high packaging density.

When ultrasonic vibration is performed as well during bonding, the head907 is composed of a horn holding section, a horn, and a oscillator,vibration generated by the oscillator is transferred to the horn, andthe ultrasonic vibration is transferred to an object to be bonded heldby the horn. The horn holding section includes a means which holds thehorn in a manner which does not diminish vibration of the horn and theoscillator. In this case, the transmissibility is determined based on afriction coefficient and a pressure between the horn and the object tobe bonded, and therefore, a pressing force is preferably controlled inproportion to the bonding area as bonding is developed. When bonding isperformed over a large area in the case of a wafer or the like, thebonding area is too large to use a horizontal vibration type ultrasonichead to perform horizontal vibration. Large area surface bonding can beachieved by using a vertical vibration type ultrasonic head. Thevibration frequency may not be particularly in an ultrasonic region,though it is herein called ultrasonic vibration. Particularly in thevertical vibration type, even a low frequency is sufficiently effective.

Although wafers have been described as objects to be bonded in theabove-described embodiment, a chip and a substrate may be used. Anobject to be bonded is not limited to a wafer, a chip, and a substrate,and may be in any form.

Note that a means for holding an object to be bonded is desirably of anelectrostatic chuck type, or may be of a mechanical chuck type.Preferably, objects to be bonded sucked and held by vacuum are tightlyattached together in the atmosphere before mechanical chucking,resulting in an improvement in tight attachment.

Although the head has the aligning/moving means and the lifting/loweringaxis and the stage has the sliding axis in the above-describedembodiment, the aligning/moving means, the lifting/lowering axis, andthe sliding axis may be assigned to the head and the stage in anycombinations, or may overlap between the head and the stage. The headand the stage may not be arranged vertically, and may be arranged in anyarrangement directions such as laterally or slantingly.

When plasma cleaning is performed while the stage is being moved, sincethe head and the stage have similar electrode shapes and peripheralshapes, electric field environments thereof are similar to each other.Therefore, separate matching boxes for automatically controlling aplasma power supply may not be used, and a single matching box can beused to change electrodes, so that cleaning can be sequentiallyperformed on the head and the stage. As a result, a compact size and areduction in cost can be achieved.

Others

Note that the present invention is not limited to the above-describedembodiments, and various other changes can be made without departingfrom the scope of the present invention. For example, in the firstembodiment, the same apparatus performs a batch process including from asurface activating treatment (cleaning) of objects to be bonded tobonding of the objects to be bonded. Alternatively, the surfaceactivating treatment of objects to be bonded using an energy wave andthe bonding process of the objects to be bonded may be performed byseparate apparatuses.

In the above-described embodiments, an elastic material may be providedon a surface of at least one of the objects-to-be-bonded holding means(the head or the stage), and when objects to be bonded are bondedtogether, pressing may be performed via the elastic material withrespect to both the objects to be bonded. With such a configuration, itis possible to increase the parallelism of the objects to be bonded.Also, it is possible to increase the flatness if an object to be bondedis thin.

In the above-described embodiments, the object-to-be-bonded holdingmeans may be held on the stage and/or the head via a spherical bearing,and objects to be bonded may be contacted and pressed by each otherduring or before bonding so that the tilt of at least one of the objectsto be bonded can match the tilt of the other. With such a configuration,bonding can be performed, increasing the parallelism (see FIG. 29).

By providing an ultrasonic transmitter or a horn instead of theobject-to-be-bonded holding tool, ultrasonic vibration is appliedinstead of heating during the bonding, thereby making it possible tomore easily achieve metal bonding in a solid phase. In this case,bonding can be achieved at low temperature or room temperature, so thatmetal bonding can be achieved in a solid phase without an influence ofthermal expansion. By suppressing an amplitude to a small level andapplying vibration after pressing, high-accuracy mounting can beachieved without a position error.

A method and a bonding apparatus may be provided in which an ultrasonicvibration head comprising a horn, a horn holding section, and anoscillator is provided, and ultrasonic vibration having an amplitude of2 μm or less is applied to objects to be bonded in the atmospheric airduring bonding, so that metal bonding is performed in a solid phase,where a load is 150 MPa or less and heating is at 180° C. or less. Whenbonding is performed in the atmospheric air, bonding is more easilyachieved by applying ultrasonic vibration. Since surface activation hasalready been performed, only a small level of ultrasonic energy isrequired, i.e., an amplitude of 2 μm or less which can suppress damageand position error, is sufficient. More preferably, the amplitude is 1μm or less. Also, by applying ultrasonic waves, a bonding load can bereduced by half, i.e., to 150 MPa or less. When bonding is performedwith respect to a metal (gold) protrusion, bonding can be achieved usinga pressing force of as high as about 300 MPa at room temperature. If abump is present on a semiconductor circuit surface, some circuits aregenerally damaged with 200 MPa or more. Experiments were conducted underthe following conditions: a gold bump (metal protrusion) having 50 μmsquare and 20 μm in height is provided on a semiconductor chip, where avariation in bump height is 1 μm, and the semiconductor chip is bondedonto a thin gold film substrate using ultrasonic waves (ultrasonicbonding) or at room temperature (room-temperature bonding). In the caseof the room-temperature bonding, bonding was achieved when the load was80 g/bump or more. In the case of the ultrasonic bonding, bonding wasachieved when the load was 40 g/bump or more. Therefore, the bump needsto be crushed by 1 μm or more as a crushed bump amount. When a bumphaving a height of 20 μm is produced by gold plating, the lower limit ofa variation in height is 1 μm. Therefore, it is necessary to crush thebump in such an amount.

INDUSTRIAL APPLICABILITY

Note that the present invention is not limited to the above-describedembodiments, and various changes can be made with respect to theabove-described embodiments without departing the scope and spirit ofthe present invention. The present invention can be widely applied tobonding of a plurality of objects to be bonded, such as a wafer and thelike, particularly preferably a MEMS device.

1. A bonding method for bonding objects to be bonded having a bondingportion formed of metal, comprising the following steps: (a) treatingsaid bonding portions of said objects to be bonded with an energy wavewhich is an atom beam, an ion beam, or a plasma to thereby clean thebonding portions of adhering substances; (b) contacting said bondingportions of said objects to be bonded with each other in a low vacuum of10⁻⁵ Torr or more in the atmospheric air; and (c) crushing minuteirregularities on a bonding surface of the bonding portions in contactwith each other to thereby bond the objects to be bonded together,wherein said bonding portions of objects to be bonded are formed ofgold, after step (a) and prior to step (b) at least some of the adheringsubstances readhere to the bonding portions to thereby form an adheringsubstance layer, step (c) causes a bonding interface between the bondingportions to spread by spreading the adhering substance layer whichcauses a new gold surface to appear at the bonding interface so thatbonding is achieved between the bonding portions, and steps (b) and (c)are each performed in a solid phase at a temperature between roomtemperature and 180° C.
 2. A bonding method for bonding objects to bebonded having a bonding portion formed of metal comprising: (a) treatingsaid bonding portions of objects to be bonded with an energy wave whichis an atom beam, an ion beam, or a plasma, to thereby clean the bondingportions of adhering substances; (b) contacting said bonding portions ofobject to be bonded with each other in a low vacuum of 10⁻⁵ Torr or morein the atmospheric air; and (c) crushing minute irregularities on abonding surface of the bonding portions in contact with each other tothereby bond the objects to be bonded together, wherein each of saidbonding portions is formed by forming a gold film in a solid phase on asurface of a base material having a hardness of 200 Hv or less, afterstep (a) and prior to step (b) at least some of the adhering substancesreadhere to the bonding portions to thereby form an adhering substancelayer, step (c) causes a bonding interface between the bonding portionsto spread by spreading the adhering substance layer which causes a newgold surface to appear at the bonding interface so that bonding isachieved between the bonding portions, steps (b) and (c) are eachperformed in a solid phase at a temperature between room temperature and180° C., and after said objects to be bonded are bonded together in step(c), said gold film is diffused into said base material.
 3. The bondingmethod according to claim 2, wherein said object to be bonded is asemiconductor or a MEMS device in which said bonding portion comprises aplurality of metal bumps formed by forming said gold film on a surfaceof said base material, and said base material is copper, and after saidobjects to be bonded are bonded together, said gold film is diffusedinto the base material.
 4. The bonding method according to claim 1,wherein said energy wave is a low-pressure plasma.
 5. The bonding methodaccording to claim 4, wherein at least one of said objects to be bondedis a semiconductor; and said bonding portion of each of said objects tobe bonded is subjected to plasma cleaning using said low-pressure plasmawhich is generated with an electric field having alternating + and −directions generated by an alternating power supply before said objectsto be bonded are bonded together in a solid phase at room temperature.6. The bonding method according to claim 5, wherein said alternatingpower supply is an RF plasma generating power supply capable ofcontrolling a value of a bias voltage Vdc.
 7. The bonding methodaccording to claim 5, wherein said alternating power supply is a pulsedwave generating power supply capable of controlling a pulse width. 8.The bonding method according to claim 1, wherein said bonding portion ofat least one of said objects to be bonded has a surface roughness Ry of120 nm or more.
 9. The bonding method according to claim 8, comprising:a head for holding one of said objects to be bonded; a stage for holdingsaid other object to be bonded; and a vertical drive mechanism forperforming a position control with respect to at least one of said headand said stage in a direction substantially perpendicular to saidbonding surface of said object to be bonded, and performing a pressingcontrol, wherein, when said objects to be bonded are bonded together,during the bonding, said vertical drive mechanism is driven to presssaid objects to be bonded, and thereafter, said vertical drive mechanismis stopped to hold a constant height of said head from said stage for apredetermined time.
 10. The bonding method according to claim 1,wherein, after said bonding portion of at least one of said objects tobe bonded is subjected to leveling, said bonding portion of each of saidobjects to be bonded is treated with said energy wave, and thereafter,said objects to be bonded are bonded together in a solid phase at roomtemperature.
 11. The bonding method according to claim 10, wherein saidleveling is performed using said opposing object to be bonded beforesaid objects to be bonded are bonded together.
 12. The bonding methodaccording to claim 1, wherein in a chamber having a reduced pressure,while said bonding surfaces of said objects to be bonded are not placedfacing each other, said bonding portions are treated with said energywave, and thereafter, at least one of said objects to be bonded is movedso that said bonding surfaces are placed facing each other, andthereafter, at least one of said objects to be bonded is moved in adirection substantially perpendicular to said bonding surface to contactsaid bonding portions with each other, and bond said objects to bebonded together in a solid phase.
 13. The bonding method according toclaim 1, wherein, when said bonding portion is treated with said energywave, a metal electrode is provided at a position facing said bondingsurface of at least one of said objects to be bonded, a metal filmincluding a metal forming said metal electrode is formed on said bondingsurface of said object to be bonded by sputtering, and said objects tobe bonded are bonded together in a solid phase.
 14. The bonding methodaccording to claim 1, wherein said bonding portion is formed in theshape of a contour, said bonding portion is surface-activated with saidenergy wave, and thereafter, said objects to be bonded are bondedtogether in a solid phase at room temperature, so that space surroundedin said shape of contour by said bonding portions is formed between saidbonding surfaces of said objects to be bonded to enclose a predeterminedatmosphere in said space.
 15. The bonding method according to claim 14,wherein said bonding portion is formed on a surface of a base materialhaving a hardness of 200 Hv or less, and said bonding portion of atleast one of said objects to be bonded is a gold plating having athickness of 1 μm or more.
 16. The bonding method according to claim 14,wherein bonding is performed in a vacuum, so that a vacuum atmosphere isenclosed in said space.
 17. The bonding method according to claim 14,wherein, after said surface activation of said bonding portion, a vacuumstate of a low-pressure chamber is replaced with filling gas, and saidobjects to be bonded are bonded in said filling gas to enclose saidfilling gas atmosphere in said space.
 18. The bonding method accordingto claim 1, wherein said objects to be bonded are bonded together in theatmospheric air.
 19. The bonding method according to claim 18, whereinone of the objects to be bonded is an electrically functioning devicewhich employs the bonding portion as an electrode, and said bondingportion has a surface formed of gold, said bonding portion of the objectto be bonded is cleaned with said energy wave, and thereafter, anattached layer is formed on said bonding portion using gas, said bondingportions including an metal electrode are contacted with each other inthe atmospheric air, the positions of said objects to be bonded areadjusted to optimum positions while said device is caused toelectrically function, and thereafter, said objects to be bonded arebonded together in a solid phase at room temperature.
 20. The bondingmethod according to claim 18, wherein one of said objects to be bondedis a chip, and said other object to be bonded is a wafer on which aplurality of said chips are to be mounted, and a plurality of said chipsare continuously bonded to said wafer.
 21. The bonding method accordingto claim 20, wherein, during the time when said chips are continuouslybonded to said wafer, after a predetermined time has passed, said waferis treated again with said energy wave, and thereafter, bonding of saidchips to said wafer is resumed.
 22. The bonding method according toclaim 1, wherein said object to be bonded is a chip or a wafer composedof a semiconductor or a MEMS device.
 23. A bonding method for bondingobjects to be bonded which have a bonding portion formed of metal,comprising: (a) treating said bonding portions of objects to be bondedwith a plasma to thereby clean the bonding portions of adheringsubstances; (b) contacting said bonding portions of said objects to bebonded with each other in a low vacuum of 10⁻⁵ Torr or more in theatmospheric air; and (c) crushing minute irregularities on a bondingsurface of the bonding portions in contact with each other to therebybond the objects to be bonded together, wherein said bonding portions ofobjects to be bonded are formed of gold, after step (a) and prior tostep (b) at least some of the adhering substances readhere to thebonding portions to thereby form an adhering substance layer, step (c)causes a bonding interface between the bonding portions to spread byspreading the adhering substance layer which causes a new gold surfaceto appear at the bonding interface so that bonding is achieved betweenthe bonding portions, and steps (b) and (c) are each performed in asolid phase at a temperature between room temperature and 180° C.